The importance of headspace.

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dellet
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The importance of headspace.

Post by dellet »

We all seem to know how important headspace is, but what about “consistent headspace” and how tight of a tolerance do we really need.

I’ve been in a rimfire wormhole lately and took on a new project. It’s an old gallery rifle that was actually set up quite well. The problem is it isn’t chambered in 22 short. Not a lot of ammo choices, so making the most out of what’s available is about all you can do.

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One of the tools available is a rim thickness gauge, or headspace comparator.

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I sorted rounds at about .0005”. The dial on the gauge is big enough to read halfway between marks and found thickness to be +/- .001. These were CCI Target loads with an advertised velocity of 850 fps.

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The left hand group had one each of the five sorted sizes, the group on the right were all the same thickness. This was consistent over 5 pairs of 5 shot groups. All groups were shot at 50 yards.

The target below is a good representation of a regular group on the left and a sorted group on the right. The slightest wind is tough to deal with when shooting a 29 grain bullet around 900 fps.

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Sorting probably reduced group size 25-30%, mostly vertical. I chose a rifle and cartridge that I felt would be most likely to show improvement. Bullet weight and velocity can cover for a lot of poor loading practices. With rimfire sorting is about all you can do. Headspace, cartridge weight, base to ogive. I think this is a bit of an eye opener on some thing I might take for granted.

A lot of shooters get caught up in a small group and never experiment or apply what helps other disciplines. I think that is problem. A lot can be learned stepping outside the box.
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TRshootem
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Re: The importance of headspace.

Post by TRshootem »

At more than a decade ago, I read a piece about the rim thickness measurement and the tool used. I think it was in Precision Shooting magazine. I was fascinated by both the technical explanation and the results. I wish I had kept those issues, one can only squirrel away just so much before the lady of the house begins to question your hoarder status. I still have some .22 Short ammo somewhere in my stash...

Very cool project, thanks for showing us what you're working on these days.

TR
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rebel
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Re: The importance of headspace.

Post by rebel »

All dellet needs is an excuse to buy another cool firearm related tool. :lol: :mrgreen:
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rebel
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Re: The importance of headspace.

Post by rebel »

Do not any of you reloading newbies see the implications of this? Do you not see that this applies to center fire as well? Or are you just content to sit back and and ask questions that can be found with a simple search? Curious to the lack of views and comments.
Sorry to sound like an A hole, but a bit tired of the "what's your load shit". Would really like to see a complete understanding of the dynamic here.
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GregP42
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Re: The importance of headspace.

Post by GregP42 »

It is something I have seen shooting small bore IHMSA over the years, and with centerfire bolt guns if the cases have been sized too much you get bad groups. ARs I have to make sure they all are the same size, but small enough to feed no matter how fouled they get.

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dellet
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Re: The importance of headspace.

Post by dellet »

The concept has probably been around for at least 100 if not 150 years or more. I just see new parallels with old equipment. Until looking for “Match Grade” 22 short, I had know idea production basically stopped about 15 years ago. Rules for Olympic handgun competition changed and the shorts are no longer used.

Most common way of selection Match grade ammo for 22 LR is buy a bunch of samples, find what shoots best in your rifle, then buy as much of that lot as you possibly can.

With little or no choice in ammo for this rifle, the question becomes “how to maximize what you have”.

I tried sorting by weight, with little success. The whole round weighs in around 38.7 grains and only varied about .3 grains in 100 rounds checked. I found no apparent advantage. That may change when used as a second tier of separation instead of first.

Sorting by rim I found 5 basic thicknesses. Interestingly enough what became the “0” had the most rounds, 127/200. The rest were +/- .001”. Rounds were sorted in .0005” increments. The above group represents five rounds where headspace varied only .002”. Which interestingly enough is the magic number the precision guys often use as the amount of setback when sizing.

Next step will be to measure the actual headspace with the “0” cartridges and compare the relative accuracy of each thickness and hopefully establish a measurement of “best” headspace.

Then there might be sorting base to ogive in there someplace or time.
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Ben B.
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Re: The importance of headspace.

Post by Ben B. »

I used to shoot rimfire benchrest, which is a pretty dern precise game with a 0.10” bullseye at 50 yds, and eventually geared up with most, certainly not all, of the toys. The general finding back then was that sorting, whether by weight or rim thickness, usually improved “cheap” .22 ammo, and wasn’t worth the time for Eley black box and grades above that.

Last I heard, a lot of the guys had stopped chasing test lots of ammo, and started having 4-5 barrels per gun, would buy a case or 2 of Eley and just switch out barrels to find one that matched that ammo. That’s when I REALLY knew I’d gotten out of the game for the right reasons!
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popper
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Re: The importance of headspace.

Post by popper »

Actually not a gallery gun but a good target rifle. Rim thickness effects 'jump' to the lands. Reloaders set this for precision but rimfire - not much choice. Tighter tolerance on rim thickness probably indicates higher quality ammo. SIL marlin 60 won't even chamber a lot of new 22lr as new stuff is larger dia. 22 short doesn't erode the throat much - I assume it really is 22 short chambered?
I want one in 30 badger or rimmed BO.
excess650
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Re: The importance of headspace.

Post by excess650 »

That appears to be a 45 pattern Stevens 44-1/2 with about 30" of barrel. Lots of folks would ask why you don't rechamber for 22LR without knowing there is a difference in barrel twist rate from S to LR.

You could find another original barrel to fit and likely reline, or send it off to CPA Rifles and have another new barrel made with a match chamber.
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dellet
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Re: The importance of headspace.

Post by dellet »

popper wrote: Sat May 02, 2020 5:00 pm Actually not a gallery gun but a good target rifle. Rim thickness effects 'jump' to the lands. Reloaders set this for precision but rimfire - not much choice. Tighter tolerance on rim thickness probably indicates higher quality ammo. SIL marlin 60 won't even chamber a lot of new 22lr as new stuff is larger dia. 22 short doesn't erode the throat much - I assume it really is 22 short chambered?
I want one in 30 badger or rimmed BO.
Gallery rifles of the time are simply indoor or short distance target target rifles, Generally defined by chanbering, and yes this is actually 22 short.

Headspace is a bit of a misnomer since in a good rimfire target or match chamber the bullet will engrave the rifling and jam. So the "headspace" is in front of the rim to the chamber instead of the bolt face.
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