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Military Firearm Restoration Corner

Headspace Quiry


cold shot

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I've finished reaming the 8mm/300 win mag . I took an R.P. nickel round and made a dummy round for checking headspace. I have the belted go/no go guages but I wanted to see how a round would chamber . My question is: The dummy round when closing the bolt is smooth and not loose or tight, but the bolt won't close with the go guage What gives, any ideas? DAVE

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What gives? The brass (belt) is on the small side. This has long been a criticism of belted magnums. The belts vary greatly in size. This also illustrates why brass is not always (almost never) a good tool to use as a headspace gage.

 

You can do what you are trying provided you get a lifetime supply of the same brass (lot) and ONLY use it. Problem is (not in this case since its a wildcat) what if you want to use factory ammo that has a thicker belt?

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OK- so if I set the headspace with the go/no go guages,will I have any problems with flashback at the bolt? I don't want any powder burns ,it will really mess up your day!

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Absolutely not.

 

The belt on a bottle-necked case with a sharp shoulder angle is worthless... The belt is a carryover from the old H&H rounds, and I believe it was for use in double rifles.

 

It was an available large-capacity case to build shorter wildcat rounds on, and factories followed suit. If you reload a 7mm Mag, .338 Mag, or whatever, you headspace on the shoulder. Look at the newest magnums... Large fat case with no belt. Even with rimmed cases, you should still headspace on the shoulder.

 

Reamers and chambers need to headspace on something, and manufacturers use the belt to headspace on when chambering. The chamber is set to a certain spec, and the base-to-shoulder distance is part of that spec. Setting the belt headspace lets all else fall in place.

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Gun Nutty- I checked ALL the brass that I will be using and they are closing just fine. I had removed .010 from the chamber face and remeasured the space from the top of the case to the barrel face and the measurement was .100" where before it was .110" the bolt closes with no forcing needed. now I'm ready to size the brass. I ran ALL the brass thru to see if any were tight or loose. Then I measured the cases form the front of the telt to the back of the case, they were all the same as when I got them,they were all from the same lot. I have 350 cases to use for my 8mm/300 win mag. ALright!!!SEE you later, you guys are great! DAVE

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The "depth" of the belt (bolt-face to forward shoulder of belt) is 0.220". I'd set things to exactly that. If you don't have a headspace guage, you can make a simple plug on a lathe... I wouldn't do it for a shoulder headspace, but for the belted case I'd feel confident enough to make one. It would be a 0.532 diameter cylinder 0.220" long. You could make another 0.222 long for a MAX.

 

You're headspacing on the shoulder when you re-size, so the belt is really irrelevant. There really isn't an advantage to setting it to the brass case.

 

I would be concerned about sizing dies. If you make the chamber too short (setting the chamber on a very short belt), the reloading dies may not hit the shoulder of a fired case. You'd have to do some grinding on the dies then.

 

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You're headspacing on the shoulder when you re-size, so the belt is really irrelevant. There really isn't an advantage to setting it to the brass case.

 

I would be concerned about sizing dies. If you make the chamber too short (setting the chamber on a very short belt), the reloading dies may not hit the shoulder of a fired case. You'd have to do some grinding on the dies then.

As you say, we are really headspacing on the shoulder, So one would not want to have the sizing die push the shoulder back at all. As long as you use that brass in that rifle... All is as good as you can get it. MV

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Thanks guys, After they are fireformed to that chamber they will ONLY cbe neck sized as it is a wildcat . The 300 win mag barrel that goes on the same action is set with go/no-go guages so if need be I can use factory ammo.The 8mm/300will be using only the brass mentioned beforehand. I have pleny of those. Dave

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