Consequences of tight Chamber?

[farmer7]

Hello, I bought a Tikka supervarmint recently in .308 and was getting some ejector marks at not particularly heavy changes using once fired Lapua cases (fired in a different rifle) which I full length sized initially before loading for this rifle. Anyway I dropped my charge by over two grains and was still getting some ejector marks.

Since then I bought a box of new Lapua brass and with my old PSS aside from the odd dinged neck they were good to go from the box after neck sizing to straighten out the case mouths but with this rifle when I drop a new piece of brass into the chamber and try and close the bolt its very tight! Some are ok but even the easiest ones to chamber have at least some resistance. And the worst ones are very, very tight.

I've obviously got a very tight chamber and have to bump the shoulders back at least 3 or 4 thou on these new case to get the bolt to close easily.

Are there any safety issues with having a tight chamber like this? Does anyone else find new brass tight to chamber?

Are there any cons to having a tight chamber?

The rifle shoots everything very very well though!

 

[Scott Harris]

Downside to tight chamber is lack of interoperability with factory and/or handloaded ammo. Also, your standard SAAMI dies may or may not work with a tight chamber. Up to you whether that is important. Personally, if I buy a rifle chambered for 308 WIN, I expect it to adhere to 308 WIN SAAMI specs. If it doesn't, I'd send it back to the manufacturer for refund or replacement.

 

[jonbearman]

I would check it with go and no go gages to be sure the rifle is out of spec.When sizing full length ,pause at the top of the strke and it will help the brass hold its proposed headspace once you remove it from the die itself.If you have the die set to just touch the shell plate,set it so you cam over with a quarter turn or lap the top of the shell plate with wet or dry paper on a piece of glass to get more set back.

 

[Turbulent Turtle]

That's not a "tight" chamber, that's a "short" chamber. The use of go/no-go gauges is definitely indicated here.

 

[farmer7]

Thanks for the replies everyone. I spoke with a knowledgeable rifle maker earlier and he was surprised that I wasn't able to easily chamber new Lapua brass.

If it is the chamber would that account for higher pressures with reasonable powder charges?

I can make them chamber easily by screwing down my Redding body die and camming over in the Forster Co-Ax but not if it is set to just firmly touch the shell plate.

I appreciate the help guys as I dont have any riflesmiths nearby.

Sorry Bayou Shooter, do you mean by this I should buy some headspace gauges?

That's not a "tight" chamber, that's a "short" chamber. The use of go/no-go gauges is definitely indicated here.

If it doesn't close on a go gauge do I have a problem? I presume it will, because it would have had to be proofed, but perhaps its on the limit?

 

[brxbrad]

Had the same problem with a tight chamber 7-RSAUM. I found that headspace wasn't the problem, I just needed to base size my brass. By the way, I was using Redding S-type Dies. You know the expensive ones.. I shaved my case holder to bump the shoulders an extra 1 to 2 thousands and ended ruining some very expensive brass trying to bump the shoulders back and it resulted in case head separation. I should have had custom dies made that matched the chamber. I thought I was doing the right thing, but......

Advice......
Talk to your smith. Don't make expensive mistakes thinking you have it figured out.
I have since retired the SAUM and I'm now moving on the path of 284 Winchester......Better barrel life, less expensive brass by 2.50 ea even using Lapua 6.5 necking it up. I've learned my lesson. Don't jump the gun....Do your homework......Ask persons with more experience before mistakes are made.

 

[Bayou]

I've obviously got a very tight chamber and have to bump the shoulders back at least 3 or 4 thou on these new case to get the bolt to close easy.

To address this problem, have you tried, or thought about trying, a RCBS small base sizer die? Could be an easy and cheap solution......

 

[ReedG]

I agree you should buy/borrow at least a "go" gauge and check the chamber. If the go-gauge allows the bolt to close without binding, then I believe you are lucky. I like a "tight" chamber because they don't let the brass expand too much on each firing. Some factory chambers allow .008 to .012 expansion and I'll take a tight chamber any time. If your FL die doesn't bring the base expansion ring down by .001" you should consider a "small base" die or custom die. Almost all custom chambers are cut to minimum SAAMI specs or less.

Having said that, I am concerned about the ejector marks on the brass as I don't believe there is anything a tight chamber will do to cause them. I caution you again to check your rifle with a go-gauge and then carefully work up your loads for this particular rifle, not presuming that loads from another gun will work in this one.

I automatically FL size all new brass before loading, so cannot tell you whether new Lapua brass should chamber or not.

 

[Turbulent Turtle]

Thanks for the replies everyone. I spoke with a knowledgeable rifle maker earlier and he was surprised that I wasn't able to easily chamber new Lapua brass.

If it is the chamber would that account for higher pressures with reasonable powder charges?

I can make them chamber easily by screwing down my Redding body die and camming over in the Forster Co-Ax but not if it is set to just firmly touch the shell plate.

I appreciate the help guys as I dont have any riflesmiths nearby.

Sorry Bayou Shooter, do you mean by this I should buy some headspace gauges?

That's not a "tight" chamber, that's a "short" chamber. The use of go/no-go gauges is definitely indicated here.

If it doesn't close on a go gauge do I have a problem? I presume it will, because it would have had to be proofed, but perhaps its on the limit?

The thing that bothers me is that you say it does not close easily on virgin Lapua brass. I have a tight chamber on my F-TR rifles, but they close perfectly on virgin Lapua brass. I only bump back the shoulder about .001 to .002 from a fired case and I also use a Redding Small Base Full Length S-type bushing die. The small base only helps controlling the OD towards the base of the cartridge; it will do nothing to shorten the cartridge.

Yes, I believe you may have a headspace problem and if you do not want to buy a Go-guage, just buy some factory ammo and see if you can chamber and fire that. There should be virtually no resistance when closing the bolt on factory ammo, virgin Lapua brass or properly resized fired cases. If there is resistance, you have a problem; it could be a too short leade or a short headspace issue.

 

[searcher]

I recall the first time I ordered a custom barrel already chambered (Shilen) for a varmint rifle. It was for a .223 in a "Match chamber". I had another gunsmith put on a muzzle brake and some other work and he decided to go ahead and assemble it for me. He called me, telling me he had some "bad news', in that the chamber was out of spec and that the bolt would not easily lock up on the "go" guage with the factory ammo he was using to test it. I drove over and, seeing that it would close when allowed to lock up under recoil, and knowing it was a Match chamber, I called Lilja to confirm my suspicions - that "standard" go/no-go guages were NOT suitable for a Match-type chamber due to the "tight dimensions". This is particularly so in .223/5.56 and .308 chambers. If checking with guages, get those meant for Match chambers. Brownells sells them. I doubt you need them.

Because the shoulder needs to be bumped a few thousandths to get the bolt to close with no resistance is of no real concern I believe. This would obviously be a concern if the same circumstance was present when trying to load factory ammo - and if factory ammo was to be used in the future - or could be. I would just about bet this gun will have no problem accepting factory ammo and that is easy enough to test. I'd also have no problem just bumping the shoulder back on the Lapua brass the first time or full-length sizing once-fired brass from someone else's gun the first time.

The extractor/ejector marks are a separate issue and could be caused from a number of common encounters. I'd first look at:
* Does the sized case easily slide into and out of the chamber?
* Verify necks are properly trimmed to length AFTER sizing
* Do a chamber casting to see the actual neck diameter as compared to
a loaded round
* Run your load over a chronograph. This will tell you volumes as to whether
you are overloaded or have a problem.
* Double-check the headspace of your loaded round vs a fired case. Note that
if you have excessive headspace, the proper headspace cannot always be
attained on the next firing without the bullet touching the lands so that the
case is held against the bolt face when firing - thus allowing the shoulder
to get blown forward.

All said - I doubt there is anything wrong with your rifle unless it won't load factory ammo. Even though i don'[t shoot factory stuff - the next owner might want to.
Once you eliminate any problems with neck diameter, case length, headspace and have determined that your load is shooting within acceptable velicities, I wouldn't think your gun would have any issues. If it continues to show pressure signs with velocities in check - THEN I would be concerned to think there may be a problem.
* Shoot over a chronograph to see whet

 

[spclark]

If this is a "factory new" rifle, get a Cerrocast of the chamber made to check critical dimensions at the case web and shoulder. Knowing neck diameter won't hurt either, along with where the neck ends & the freebore begins or what's called Case Overall Length.

If standard 308 GO gauge won't allow for easy bolt lock-up, that chamber's undersize somewhere.

New brass is typically short in several dimensions so as to fit a wide variety of chamber profiles, within reason. There's no practical need to bump shoulders in virgin brass other than to make a case fit a "standard" chamber where otherwise it wouldn't.

If that rifle's not fresh from the factory it may have had a barrel with a non-standard chamber fitted somewhere along the line.

 

[bigedp51]

If it doesn't close on a go gauge do I have a problem? I presume it will, because it would have had to be proofed, but perhaps its on the limit?

farmer7

Is the rifle brand new and are you the first owner of this rifle, do your proofing laws still require reproofing of new firearms or when a firearm changes hands. Meaning is a brand new rifle required to be inspected before sale?

I find it strange that a Finnish made Sako rifle will not chamber Finnish made Lupua brass, meaning quality is always very high from this country.