? on accuracy: OAL vs deadspace

[HMdoc]

I need some guidance. Accuracy is increased if the reload is set to about .020-.040 from the lands. But this setup leaves some deadspace between the powder and the bullet. Going for accuracy, and fit in the magazine/clip is not an issue, is it more accurate to reload closer to the rifle lands but with deadspace or better to not have any or less deadspace as long as the OAL is within acceptable limits? Thanks.

 

[ksnecktieman]

I ws in a conversation about this recently, kind of. I am a listener, and I was talking to an experienced reloader. "Freebore" is the term we were discussing. That is how far the bullet has to jump to get to the lands of the rifling at the front of the chamber. His expressed conviction was that every rifle is different in how much freebore it likes. He mounts his selected bullet in a cartridge, chambers it, and measures it. Then he loads a variety of lengths in five thousandths of an inch shorter than that and tests them. He said one of his rifles likes up to .030 (thirty thousandths) of freebore, and one likes to have the projectile touching the lands when chambered. He said the guys he knows that are shooting the weatherby mag cartridges with the really steep shoulder seem to prefer a lot of freebore. I did not think to question him about the powder volume behind them. I think I will ask him if he has changed the powder behind them to see if different ones require different freebore.

 

[Vern Humphrey]

It seems we have several terms here -- what you call "dead space" is "powder space" -- that is, unused space in the case. In general, a full case tends to be a bit more accurate than one that has a lot of unused space. In some cases, the powder can take up so little space that the orientation of the cartridge before firing can markedly affect accuracy -- hold the weapon muzzle up, then bring it to firing position and you get one point of impact, hold it muzzle down and you get another.

"Freebore" is a gap between the bullet at rest and the lede (the origin of the rifling.) In some rifles, freebore is built-in (Weatherbys used to be famous for this.) In general, most rifles will shoot better if there is relatively little freebore -- that is, if the shoulder of the bullet (the fartherest forward full diameter portion of the shank) is quite close to the lede. Stony Point makes a comparator -- a measuring device that will let you accurately determine how close your load positions the bullet to the lede.

In most rifles, seating the bullets close to the lede is more conducive to accuracy than reducing excess powder space. If you think powder space is your problem, try shooting a dozen rounds over a chronograph -- one symptom of excess powder space is a wide variation in shot-to-shot velocity.

In your case, you have answered your own question, "Accuracy is increased if the reload is set to about .020-.040 from the lands." The gun is telling you what it likes.

 

[HMdoc]

Thanks for the replies. I am currently reloading for my M1 garand using 47 gr IMR 4895 with Sierra 168 HPBT. According to the Speer manual that i am using, the OAL should be 3.295 (max is 3.34). Using a Stoney Pt OAL gauge, my M1's OAL is way passed the max of 3.34. Even with a max of 3.34, it is still at least 0.10 less than the Stoney Pt gauge with bullet comparator. I understand that since my M1 still has the stock barrel and not a match barrel maybe(?) it is made for "looser tolerances." If so, should i stay with 3.295 or max it out to 3.34. Will i get an increase in accuracy by maxi-ing it out to 3.34 (do i dare go past that for even more accuracy)?

Vern, i got that "accuracy is increased ..." from Stoney Pt, sorry I did not clarify.

 

[Vern Humphrey]

Quote:
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Vern, i got that "accuracy is increased ..." from Stoney Pt, sorry I did not clarify.
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Ah. I think what I'd do is simply try it then in that case. Your load is right on for the M1, and no on I know reports problems with excess powder space with that load.

If you have stoppages and feeding problems, they may be related to excess OAL, but if not, you're fine.

 

[taliv]

if it's bugging you, just go with a slower-burning powder and take up some of that space.