Sage's 7mm aluminum gas checks

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mtngun
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Sage's 7mm aluminum gas checks

Postby mtngun » Sun May 05, 2013 9:51 am

Gas checks have been in short supply lately so that seemed like a good excuse to experiment with aluminum checks. http://www.sagesoutdoors.com/index.php?

The Sage checks are 0.079" deep vs. 0.055" for a Hornday check.

The Sage checks weigh 1.3 grains vs. 3.9 grains for a Hornady check.

The Sage checks are 0.017" thick vs. 0.0185" for a Hornady check.

The Sage checks are 0.283" - 0.284" OD vs. 0.288" for a Hornady check.

They were advertised to fit a 0.253" shank, but I installed them on my latest experimental 7mm bullet which has a 0.250" x 0.080" shank. Normally I cut 7mm shanks to 0.251" for customers, but I prefer an easier fit for my personal use.

The Sage checks were a snug fit on my 0.250" shanks. I could start them by hand, but had to use a seating die to finish the job -- though only modest effort was required to seat them. I can't imagine installing these on the recommended 0.253" shank -- their ID is too small for that. After sizing to 0.2855" the checks felt tight and I could not spin them.

Hornady checks were an easy fit on my 0.250" shanks. I could install them by hand and no seating die was required. After sizing to 0.2855", I could spin the checks but they were in no danger of falling off -- a perfect fit as far as I am concerned.

However, after I oven treated the checked bullets, several of the aluminum checks fell off. I re-installed and resized the check and it stayed on. Maybe the aluminum check was "opening up" due to the heat ?

The installed diameter of the Sage check was only 0.283" - 0.284". That's partly because of my 0.250" shank, but it's also due to the thinner metal. 0.250" + 0.017" + 0.017" = 0.284". That's just math. IMHO the metal should be thicker, 0.0185" similar to the Hornady checks, so that the check will crimp on tightly even in an oversize die.

I doubt if the slightly thinner material will make an iota of difference in how they shoot, since the check will obturate to fit your gun when the cartridge is fired, but you may see a difference in how the check fits at the loading bench.

I'll do a shootout later this week and we'll find out if there is a difference in accuracy. I'm a little worried about aluminum fouling at my velocities, but we'll see. Years ago, I used homemade beer can checks in revolvers with complete success, so I don't doubt that aluminum checks can do the job providing aluminum fouling isn't an issue.
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mtngun
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Location: Where the Salmon joins the Snake

Re: Sage's 7mm aluminum gas checks

Postby mtngun » Sun May 12, 2013 1:08 pm

Shootout done, using experimental bullet 7EL3 in the 7-30 Contender Carbine. Load data for both bullets as follows:

42 gr. WW760
WLRM primers
2.52" COL
HVR lube
heat treated WW & Sn alloy
120.3 gr. ready to shoot with Hornady check, less with Sage check

I started with a clean barrel, shot five 3-shot groups at 100 yards with the Hornady check without cleaning. Average 2.71", 2646 fps.

Then I cleaned the barrel and repeated the process with the Sage check loads. Average 6.99", 2655 fps.

The Sage check accuracy started out OK but deteriorated as more shots were fired. The difference in accuracy was statistically significant using a t-test. http://www.graphpad.com/quickcalcs/ttest1.cfm
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Group #4 shot with Sage checks. Accuracy was definitely deteriorating at this point.
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Another odd thing about the aluminum checks is that they sometimes generated a significantly larger secondary pressure spike. Here's a few traces for the aluminum check with secondary spikes running 35K - 50K.
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And here's traces with the Hornady check and it's secondary spike is only 20K - 25K.
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Conclusion: The aluminum checks seem to foul the barrel and hurt accuracy at 2650 fps. I cannot recommend them for high velocity rifle applications, though I suspect they'd work just fine at handgun velocities.

There was no evidence that the aluminum checks were coming off in flight, even though they were a bit undersize and seated into the powder space. If they were coming off, I'd expect them to hit the chronograph once in a while, and that never happened. Also I'd expect to find the occasional check 25 - 50 yards downrange, but I looked and didn't see any.

I'm not sure what, if anything, the larger secondary spikes mean, but there was definitely something going on there.


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