Establishing Headspace-Finish Reaming

Just completed finish reaming 2 Garands which I recently re-barreled, a SA 4.3M with a new SA 4-52 barrel, and a SA 5.9M with a used, but lightly worn HRA 6-52 barrel. I used post-war SA bolts correct for the serial numbers and cut the chambers with a Clymer pull through reamer.

There are often discussions about dimensions of Forster vs Clymer headspace gauges and I thought folks might find it interesting that the Clymer reamer cuts the chamber to conform to a US GI "go" headspace gauge, while the bolt will close on a Forster "go" gauge before reaming is completed and the right bolt lug has not made contact with the receiver rail. This tells me that a Forster "go" gauge is shorter than a GI "go" gauge and that the chamber will be cut short if one uses the Forster gauge to determine when "go" headspace has been established.

This is the second new SA 4-52 barrel that I have installed and I found that only a small amount of finish reaming was necessary for both barrels to headspace properly. Altho used, the HRA barrel required much more reaming than any new GI barrel that I've installed. I extracted and cleaned the reamer and chamber and ran a headspace check 4 times before reaming was completed. There was quite an accumulation of cuttings on the shoulder portion of the reamer each time that I checked it.

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Originally Posted by purple

Just completed finish reaming 2 Garands which I recently re-barreled, a SA 4.3M with a new SA 4-52 barrel, and a SA 5.9M with a used, but lightly worn HRA 6-52 barrel. I used post-war SA bolts correct for the serial numbers and cut the chambers with a Clymer pull through reamer.

There are often discussions about dimensions of Forster vs Clymer headspace gauges and I thought folks might find it interesting that the Clymer reamer cuts the chamber to conform to a US GI "go" headspace gauge, while the bolt will close on a Forster "go" gauge before reaming is completed and the right bolt lug has not made contact with the receiver rail. This tells me that a Forster "go" gauge is shorter than a GI "go" gauge and that the chamber will be cut short if one uses the Forster gauge to determine when "go" headspace has been established.

This is the second new SA 4-52 barrel that I have installed and I found that only a small amount of finish reaming was necessary for both barrels to headspace properly. Altho used, the HRA barrel required much more reaming than any new GI barrel that I've installed. I extracted and cleaned the reamer and chamber and ran a headspace check 4 times before reaming was completed. There was quite an accumulation of cuttings on the shoulder portion of the reamer each time that I checked it.

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I just cut the chamber deeper on a Super Match from SA Inc that I had to do a light rebuild on. It has about 20 rounds through it. I rebuilt it because it had excessive windage when a mechanical zero was set (about 3 minutes plus at 300 yards). I found that the barrel was indexed in about 1.5 degrees too far and while I had the rifle apart, after re-indexing the barrel correctly, decided that I really should check the headspace even though it was probably ok, especially since I indexed the barrel farther outward, which should lengthen the chamber..not much, but it's certainly not going to be the same length, or shorter, in any case. Well, with a Clymer .308 Go Gage in the rifle, the bolt lug would not drop all the way down to touch the locking lug recess. It looked to be about .001" short of headspace (approximately). I thought "how could that get out of the shop?". Well, I thought, because maybe nothing was wrong when the technician cut the chamber and assembled it (sort of). I thought, if the gage used said it was good, even if it wasn't, who would know that it really was short of headspace? Well, nobody that checked it with the same gage, or same type would know. SA Inc. can normally tell you on the tag that the rifle leaves the shop with, if the chamber is 1.630, 1.631, 1.632, etc. The only company I know of that has headspace gages ready made in .001 intervals is Forster. Maybe one can draw a conclusion here, maybe not. When I reamed the chamber with my headspacing reamer which I bought from Dave Manson, it took a bit of cutting to get the bolt to drop all the way down. In fact, I had to switch from the .250 thrust bushing to the .251 that I bought from Dave recently When I did the first bit of cutting with the .251 bushing, it just went a bit beyond dropping all the way down. I think if I would have let the reamer spin a bit with the .250 bushing in place, that would have been just enough to let the bolt drop all the way, but I didn't try that. I can see that the reamer and thrust bushings seem to correspond pretty closely to each other, but none of that equipment corresponded closely to what came out of SA Inc. and should have been proper headspace. I'd really like to know what SA Inc. is using for headspace gauges.

Very interesting,

Danny

Quote:
"There are often discussions about dimensions of Forster vs Clymer headspace gauges and I thought folks might find it interesting that the Clymer reamer cuts the chamber to conform to a US GI "go" headspace gauge, while the bolt will close on a Forster "go" gauge before reaming is completed and the right bolt lug has not made contact with the receiver rail. This tells me that a Forster "go" gauge is shorter than a GI "go" gauge and that the chamber will be cut short if one uses the Forster gauge to determine when "go" headspace has been established."

Maybe I'm missing something here...You say the bolt will not close on the "go" gauge "before the reaming is complete" ...sounds right to me. It sounds like you are using a "pull through" reamer system to judge a "go" headspace gauge. Headspace gauges are far more accurate than reamers. If it were the other way around, we wouldn't need headspace gauges to rebarrel an M1. I have rebarreled dozens of M1's using G.I. barrels and have yet the see one that needed a reamer. You were just un-lucky with both of your's needing reaming.

Nope,I said the bolt WILL close on the Forster "go" gauge before reaming has been completed(as indicated by the bolt lug making contact with the receiver rail). The bolt will only close on the GI "go" gauge after reaming has been completed,which is the desired outcome. I think that I am correct to deduce that the Forster "go" gauge is shorter than the GI gauge on the basis of this experience. I don't have a Clymer "go" gauge and would like to have done a check with one of these as well. And yes, I too use headspace gauges as the definitive indicator of headspace status.
By my records I have now rebarreled 24 Garands, including 6 with new GI barrels. All new barrels and one used barrel have required reaming to establish the proper headspace,altho both of the previously mentioned SA 4-52 barrels would accept the "go' gauge w/o reaming when a worn bolt was trial fitted. In the case of my recent installation I wanted to match a correct bolt to the receiver, so I did not use the worn bolt which was a mis-match.

Recently had a new (new to me, but used USGI barrel) barrel put on. The bolt just closed on the GO gage (don't know whether my smith used a Forster or Clymer). Rather than finish ream the barrel, my smith lapped the bolt lugs. I now have 100% contact on the right lug and about 80% contact on the left lug. Something to consider if you're real close.

Don

I think I understand what you are saying now. In your first post you said
"while the bolt will close on a Forster "go" gauge before reaming is completed and the right bolt lug has not made contact with the receiver rail." I took that to mean that the bolt would NOT close on the gauge. (lug NOT in contact with the rail)

I used Clymer pull-thru reamer and go/no-go gauges for my .308 Win Garand, and I still had to shim the pull-thru reamer to get it to close on Clymer's go gage. Sometimes gun-smithing is more "art" than "science"......

Mike D