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Discussion Starter #1
I am a little fuddled. Bought a Hornady OAL gage in order to produce the best ammo possible for each weapon. Recently I was checking my setup for my 22-250 Ruger American. The specs for the OAL of the 22-250 is 2.350. When I check the setback via the Hornady OAL gauge the OAL is 2.460 before touching the throat. I have checked four manuals and the OAL is constant at 2.350. What should I do to ensure the best ammo possible?
I am using a Serria 68 HPBT as the bullet and the case has been checked and is in spec.
I would like any input as to addressing this problem. I was under the impression that the bullet should set back .020-.030 from the throat, correct me if my assumption is wrong.

Thanks

Larry
 

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I don't think "set back" is what you're after here. If I understand correctly, you are trying to establish proper COAL of your rounds with respect to the distance to the rifling, aka the "jump". A reasonable and safe place to start is around 0.010 to 0.015" off of the lands. A COAL of 2.350" puts the round at 0.011" off the lands. You should be just fine.

[edit: my math sucks...0.110"]
 

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I think you mean the bullet is seated so it is .020-.030 off the lands. It is a number that is goint to vary from rifle to rifle. As sparky mentioned .010 is a commonly used dimension.
 
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Discussion Starter #4
Coal was the word I needed but could not remember it.
If I understand correctly, OAL of 2.350 should be OK? But what is happening to the bullet as it jumps .100 to engage the rifling? I am completely ignorant of logic as far as this question is concerned. I am sure I am the one this is wrong, but just want to get educated.

Larry
 

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The tool you need is a bullet comparitor that will give you the critical measurement. there are quite a few on the market.
I use one made by Hornady

Lock-N-Load® Bullet Comparator
Measuring cartridge lengths across the bullet tips is not a reliable (or repeatable) method for measuring loaded rounds. Its common for variations of up to .025" to exist from one round to the next. Our Bullet Comparator measures rounds from the ogive to provide consistent, precise measurements. You can also use it to check uniformity of bullets from base to ogive.

Our Bullet Comparator easily attaches to the blade of your caliper and uses interchangeable inserts (available in sizes from .17 caliber to .45 caliber) to measure from the bullet ogive.

Used in conjunction with the O.A.L. Gauge, the Bullet Comparator provides the ultimate in precision measurement. The Bullet Comparator will properly align the O.A.L. Gauge for precise measurement using a caliper. This method allows direct comparison of your loads as you set up your bullet seating die for any selected bullet free-travel (jump).
 

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Coal was the word I needed but could not remember it.
If I understand correctly, OAL of 2.350 should be OK? But what is happening to the bullet as it jumps .100 to engage the rifling? I am completely ignorant of logic as far as this question is concerned. I am sure I am the one this is wrong, but just want to get educated.

Larry
" But what is happening to the bullet as it jumps .100 to engage the rifling? "
To answer your question, the bullet jumps .100. And no I am not being a smart a**. the reason being that many rifles work better with different amounts of " jump ".
The average person sets the bullet about .010 off the lands. Is this correct for every rifle? No it is not. It is a very good starting point and most people are happy with it , but it may not be the best. The only way to find out is to to start at .010 and work back until you find that "sweet spot " that gives you a touch more accuracy. It is trial and error until you are happy with the accuracy.
One of my target rifles is set so the bullet has to travel .500 before it engages the lands. (1/2 inch)
 

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Firearms chambers freebore/bullet jump, the distance the bullet moves forward during firing before it engages the rifling, is set by the particular manufactures. SAAMI (Sporting Arms Ammunition Manufactures Institute) will set a established free bore along with rest of the chamber dimensions and cartridge dimensions in accordance with who ever submits the cartridge for standardization. Freebore is the one dimension that firearms manufactures can and will alter. The problem with chamber freebore length is that some firearms manufactures might had learned of a ammunition manufacture who might had marketed what would be referred to as a hot/high pressure load, for a particular cartridge, in this case I’ll use the 300 Win.Mag, so the firearms manufactures will cut the freebore longer then SAAMI spec. A long freebore will drop chamber pressure because the bullet will be allowed to accelerate some before engaging the rifling, which is when peak chamber pressure usually accusers. This can lower chamber pressure depending on freebore length and type of gun powder used, by in some case as much 5000 psi, but because of the amount of freebore allowing the bullet accelerate faster during its freebore transit, will still maintain a high muzzle velocity. As an example, Weatherby has used what is considered a vary long freebore, as a result, Weatherby cartridges and rifles were always touted for their high velocity. The downside to a long freebore is that it usually doesn’t contribute to a high level of accuracy. A bullet transiting through a long freebore can engage the barrel’s bore non concentric and cause in simple terms the bullet to wobble as transits the barrel’s bore leaving the muzzle destabilized.

Another problem that can be a result of a long chamber freebore is that the rifles magazine, if it’s a repeating firearm, (I.E.,bolt/lever action, auto load) the magazine will often be shorter in length for a loaded cartridge then the freebore in the chamber. This is a concern if one handloads their ammo and want to seat just off the the rifling lands, which what most do for the highest level for accuracy. (Some will seat the bullet to just touch the lands.) This reduce the amount of runout as the bullet transits towards the rifling.

Some bullet manufactures of monolithic bullets such as Barnes X copper solids, recommend a minimum bullet “jump” of .050”. This is because of the bullet not having a lead core which can compress as it engages the rifling. The Barnes can’t, so chamber pressure will always be higher then a lead core bullet, so some jump is needed to reduce chamber peak pressure.

The final point is that with some firearms were bullet seating depth of a loaded cartridge can’t be set to accommodate accuracy mite be compromised by the magazine length. This can affect how much gun powder can be put into a cartridge case as a long cartridge and heavy long bullet mite have to be seated to accommodate the magazine which the deep seated bullet can encroach on the cartridge internal capacity. It’s a trade off.

P.S. it took me two and half hours to write this because of interruptions, so hopefully none of this is redundant.
 

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Discussion Starter #8
PRR1957, I appreciate the work that has gone into the answer to me.
Being an engineer I must ask certain questions in order to understand the thinking.
First: Freebore. You state that this dimension can be altered by the manufacturer to accommodate hot loads. I thought the idea of hot loads was to pack as much pressure/power as possible behind the bullet. I am aware that mass producers of ammo must produce a round that will fit in all chambers.
The jump, IMHO, must be held to a min. With a jump of more than a few thousands of an inch, an accurate round can not be produced.
I understand that I am not talking about the most accurate rifle, but it should be held to a standard.

Second: I know the bullet must have some gap(jump). I don't agree that the bullet must be made to accommodate the magazine. The magazine must be made to accommodate the round, at its maximum length. As I stated at the start the bullet I am using is a 68 grain HPBT, it appears that 55 grain is more common. The problem I have with a 55-grain bullet is the overall length is so much shorter than the 68-grain unit. So using the information you have written it appears that a 55-grain bullet would be a waste of time due to the long jump thus the 55-grain unit should never be used.

I am not trying to discount your answer, but I need to grasp the overall concept.

Again, thank you for the time you spent on the answers.
Thanks to all that have offered an opinion.

Larry
 

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Larry Isaacs,
First: The chamber cut by any particular gun manufacture for a specific cartridge will be in accordance with SAAMI spec so as any brand of ammunition manufacture cartridge cases will fit the chamber without any excessive tolerances. The cartridge case exterior dimensions along with an loaded over all length will also be set by SAAMI also. The freebore is up to the firearms manufacture discretion. There can be a multitude of reasons a particular firearms manufacture might want to choose a long freebore in the chamber, such as were I used the example of Weatherby’s long freebore, or it could be that a particular cartridge mite be operated at a extremely high chamber pressure, and the firearm manufacture feels that chamber pressure is at near the tensile strength/modules of the action, so they will cut the freebore longer then SAAMI spec. I should add that SAAMI will also set an upper limit for chamber pressure for a particular submitted cartridge for commercial standardization. This is so both the ammunition and firearms manufactures are working with a standardized specification. Go to the SAAMI website (saami.org) to look at any cartridge and chamber dimensions to get a better understanding of the relationship for dimensional tolerances between the cartridge and chamber. To throw in a variable is that one can have a custom firearm built with what is referred to as a tight chamber which the chamber is cut/reamed at SAAMI minimum dimensions. Also with a custom chamber the freebore can be specified by the customer to accommodate a particular bullet brand/design. This is usually for competition firearms, like benchrest, or F-Class. A minimum cut chamber will align a virgin cartridge case so it is more concentric with bore of the firearms barrel. I could go into a tight neck chamber, but that is getting into an even more esoteric discussion.

Second: The magazine lengths are set according to the particular firearms action design. Using an AR15 as an example, the magazine internal length was developed for the 223 Rem./5.56 NATO cartridge and will only allow for a loaded cartridge overall length of 2.260” maximum. Any cartridges that are to be chambered for an AR15 like the 6.5 Grendel, or 6.8 SPC can’t be loaded longer then 2.260”. If a longer cartridge is to be chamber, the firearm has to designed to accommodate a longer cartridge, hence the AR10, which can accommodate cartridges such as the 308 Win., but again, the internal length of the magazine will be a fixed length.

You stated a .224”, 68 gr HPBT. I’m assuming that is the Sierra bullet. That particular bullet was designed specifically for the AR15 magazine. The bullets nose/ogive is not as streamlined as their other bullets. That is to accommodate the magazine internal length. And as to the bullet jump/freebore that is again set according to the particular barrel or firearms manufacture. I adding this as an example of .223 Rem. chamber reamers to help illustrate the different freebore dimensions. Or to add to your confusion. Take note of dimension N. You can see the wide variations in the freebore.
70C5E741-FA1A-4975-8FF7-96A7F170BD8D.jpeg


If you have anymore questions, feel free to ask. Or I’m sure someone else will chime in on some aspect I overlooked.
 

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Larry Isaacs,
I like add that I had a Remington 700, PSS chambered in 223 Rem. This was built on the 700 short actions. In order to allow for a longer cartridge bullet seating length, I modified the internal magazine by removing the block at the back of the magazine and made a new thinner block. This allowed for a longer overall bullet seating to get the bullet closer to the rifling lead, in short, it decreased the amount of bullet transit through the freebore part of the chamber, and what a world difference that made as for accuracy. With that rifle I then was able to decrease the rifles five/ten/twenty shot groups sizes from 1/2 MOA to sub 1/8 MOA groups. Then I got stupid and sold it to finance another rifle, which turned out to a turd. :duh:
 

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I think I can answer your question quite simply, "what happens when a bullet jumps 0.100 into the lands?" Nothing. If you pull the bullet 0.10, how much of the bullet is still in the case neck being supported until it exits the neck and has engaged and is now supported by the rifling? Yes, I know the case neck has expanded and released the bullet but, that distance is probably less than the 0.10 jump unless you have a loose throat.

The distance held off the lands isn't simply to shorten the jump, it is to find that spot, that distance that the rifle likes for the bullet to have a running start. If it were just for concentricity and to merely shorten the jump, Black powder, cast bullet shooters would have that problem solved when our bullets actually engage the rifling for about that same 0.10 smokeless shooters hold a bullet off the lands. But then we're getting into differences in pressure generated and a whole slew of other interior ballistics.
 

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Are we talking about precision ammo made for one specific rifle, or basic shooting ammo made to use in any rifle? Not exactly sure where we're getting the .010 off the lands, but that doesn't necessarily h9ld true for every rifle using precision ammo. The Weatherby for example does seem to prefer a bit of bullet jump. I have a Remington that does best just at the lands while 68c15 has one that performs best with the bullet jammed into them. I've said it before and I'll say it again, your rifle will tell you what it likes best.
 

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I've said it before and I'll say it again, your rifle will tell you what it likes best.
+1. I have rifles that shoot best with the bullet just at the lands, some that like a bit of a jump, and some where the distance off the lands doesn't seem to matter. As has been noted, .010 seems to be a pretty common starting point, but it's only a starting point. :twocents::twocents: :)

Edit: Forgot; since I don't use anything hotter than medium loads, pressure isn't much of an issue.
 

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What you need to do is find the distance to the lands, write that measurement down then refer to it when you start seating your bullets.
If you change bullet designs, you'll have to measure again with the new bullet. That measurement will also tell you how much the throat has worn. Check it often.
And while you're at it, get the chamber OAL measurements also. Most chambers are cut about .020 longer that the listed MAX trim length. Knowing that will help when it comes to brass trimming or not.
I jam all my loads into the lands about .010. I only bench shoot my rifles except my gas guns. :)cool::cool:)
I have found that a given load set at .020 OFF the lands will create pressure sooner than that same load set with a jam INTO the lands and I can even go hotter with no ill effects.
I shoot all mid range loads, don't stress my brass and leave myself wiggle room just in case the weather gets hotter compared to when the rounds were loaded.
Load at 75*, it's 100*+ at the range and you can't figure out why you have to beat the bolt open??:eek::eek:;);)
 

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You'll find that the COL listed in manuals is an industry standard that allows a loaded round to be chambered in any rifle. For myself I don't really care how much a bullet jumps but I get as clost to the lands as I can without leaving land marks on the bullet. Works well for me. I had a Rem 700 in 6mm Rem years ago you didn't have to worry about it in. a round that would reach the lands would not load in the magazine! Worrying about bullet jump is probably really something competation shooter's might worry about. Hunter's don't require that much precision for hunting rifles. Probably not that necessary in varmint rifles either. Both my 243's will run right at 1/2" all day and all I do is get the bullet back off the lands just enough to eliminate the land marks on the ogive. Not much in competition but pretty hard on varmint's! Something I've noticed over the years is most reloader's chase competitive standards with rifle and skills that won't get them there! long as I get down under an inch I'm sort of happy. Yea, I'm one of those guy's chasing competative accuracy. I have neither the rifle or skills required to reach it!
 

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I do all of my load development touching the lands. After I find a good load, I will then start changing seating depth in .005 increments to fine tune the load.

This is the best way to find the lands....


 

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This comment is for rifle only, not pistol: Since some chambers are longer, you may not be able to get near them. When you try to lengthen the round, remember to keep at least a diameters worth of the bullet in the casing. Also when they are to far out, you may want to hand place them each time so the bolt doesn't have to push the concentric limits of your rounds case retention as it is fed and bumped about leaving the magazine and entering the chamber. Since the round has X amount of fps per the manual, when you lengthen it out, you are in essence having less pressure in the volume of the case where the manuals published pressure is at their oal (and fired out of their test device) so the fps drops. So as you work up the manuals powder level and say, hey, I went all the way to max and didn't see any pressure signs, that may be the reason. Don't assume this reaction as all powders behave differently and you still have to do the proper workups. Remember some powder might get spikey at different conditions so be careful. You will also see node effects. You may see two or three good accuracy results as you go up in powder. The results needed can change as your needs change. If I am shooting at 100 yards and find a node at lower powder, I don't need to go higher. If I want to shoot out long range, I will need to look at higher pressure to keep the round super sonic to reach that range. There is a price at high pressures that may lead to eating the throat more quickly. Be prepared to have to change powder and start all over, not all powder have a sweet spot for all chambers. Also the sweet spot may change in summer and winter. Also a perfect round made in the summer probably won't be perfect in the winter and one made in the winter not so great in the summer. In fact you may find a round in one season when nuts in another season.
 

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a little over a year ago i got my first rolling block rifle. i did not have any data as to oal so after slugging the barrel and sizing a bullet to the gun i gently dropped the bullet into the barrel and with my calipers measured from the rear of the bullet to chamber mouth. some math and i had the desired distance for oal to the lands. wow! this thing had a real deep chamber. i am sure way out of sammi . if there is one for this old gun. lots of work but she now shoots as good as i can make her. there is always a way, or several ways. the fun is in the finding.
just my two cents worth.

rick
 

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Discussion Starter #19
This question is starting to drift, let me see if I can pull back to the original question.
Using a Hornady OAL gauge and the appropriate shell and the 68-grain bullet. When the gauge is used and the bullet is pushed to the point of touching, that is my touchpoint.
The reading is 2.470. The reloading manuals state that the COAL should be 2.350, a difference of.120. While not going for bench rest precision I want the best I can get on a regular basis.
While the information given so far is interesting it has not answered the above question. As I recall, grcsat, said that one of his weapons had a jump of .500, OK. Others say a jump in the .010-020 is the number to try. I am good with all of the information, just don't understand the widespread.
Some have said the jump is required due to pressure, again this does not make sense to me.
It appears to me that the answers to my question may be part of the Black Magic of reloading/shooting.
It may be time to let this question die due to the widespread information, I will try different setups until I can find the best combination for my weapon.

Larry
 
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