Chamber clearance issues.

[codybrown]

First off, a little backstory.

I recently bought a rifle off gunbroker that was rebarreled to 300 rum. I checked headspace when I got it but only had a go gauge. It took .009 worth of tape on the gauge until the bolt wouldn't close. I went ahead and got a no-go gauge and the bolt would close on it. I took it apart and had a buddy at a tool and die shop run the recoil lug through a surface grinder and I reassembled it. It now closes on the go gauge, and has .002 of clearance between the go gauge and not closing the bolt.

Now that my headspace issue is solved, I started to load for it and have encountered my 2nd problem. The brass I have is trimmed to 2.8375 oal so it's under the 2.850 max oal. Case diameter with a bullet seated is .339. The neck of the brass is bottoming out in the chamber and the bolt is hard to close/open. The best I can measure I have about .060 of contact.

What's my next step? Trim the brass shorter or turn the necks are the only 2 options I can think of. Here's a couple pics.

 

[AlNyhus]

Get a chamber length gauge and determine exactly how long the chamber is. -Al

 

[Walt Krafft]

Pull the barrel, rent or buy a reamer, set the barrel back, and re-chamber making sure the chamber completely cleans up.

 

[big5ifty]

You could do a chamber cast to see exactly what you have, and show if there is anything else you missed.

I would go to a 'smith with a 300 RUM reamer. First check if the existing chamber was cut straight. It wasn't cut right, it may very well not be straight either.

If it's straight, shorten a bit off the chamber end, re-cut the chamber, and while it's on the lathe, take the opportunity to long throat it Weatherby style.

If it's not, new barrel.

 

[codybrown]

Could I use one of the ptg throat reamers to obtain the clearance I need? Even with the clearance issue the rifle will shoot .75 moa with a load worked up for a different rifle so I don't believe the chamber isn't cut fairly straight.

 

[Webster]

First off, a little backstory.

I recently bought a rifle off gunbroker that was rebarreled to 300 rum. I checked headspace when I got it but only had a go gauge. It took .009 worth of tape on the gauge until the bolt wouldn't close. I went ahead and got a no-go gauge and the bolt would close on it. I took it apart and had a buddy at a tool and die shop run the recoil lug through a surface grinder and I reassembled it. It now closes on the go gauge, and has .002 of clearance between the go gauge and not closing the bolt.

Now that my headspace issue is solved, I started to load for it and have encountered my 2nd problem. The brass I have is trimmed to 2.8375 oal so it's under the 2.850 max oal. Case diameter with a bullet seated is .339. The neck of the brass is bottoming out in the chamber and the bolt is hard to close/open. The best I can measure I have about .060 of contact.

What's my next step? Trim the brass shorter or turn the necks are the only 2 options I can think of. Here's a couple pics.

View attachment 1419834View attachment 1419835

You stated: The neck of the brass is bottoming out in the chamber and the bolt is hard to close/open. The best I can measure I have about .060 of contact.

Sounds like a bad chambering job. I would think the most common error would be running the reamer in too long or short. Maybe the gunsmith is a low budget operator and cannot afford go/no go gauges for many calibers?

• .009” of tape so a no/go gauge wouldn’t fit. Indicates the chamber was cut deeper than spec.
• A no turn chamber you should always have clearance. I definitely wouldn’t turn the necks to try to solve the problem.
• Not sure what you mean by the 0.060” measurement.
• Simple free thing to try is ruining one case by trimming 0.10” off and seeing if the problem goes away. If it’s tight trim another 0.010” off and try.
• If the neck is to long to fit in the part of the chamber that’s machined for fit how do you shove it in another 0.060” ?
• Reamers are supposed to be ground to a tight +/- tolerance. Not all reamers are the same. A fired 6BR Lapua case will not come close to chambering in my 6BRX. I have to FF with a new 6BR case. Kelbly told me they sometimes spec diameters on reamers when they buy them. Not off the shelf ones. I think it’s +/- 0.003” on the drawing.
• Are the cases oversize at the 0.200” line above the case head from hot loads?
• A chamber cast would make it easy to compare chamber to case dimensions. It shouldn’t cost a lot. Small operation gunsmith’s probably cannot do chamber cast.
• Someone on the website said the cost to rechamber is close to the cost of a new chambered barrel, I spend a lot of money to get the best barrels.

 

[codybrown]

The .060 measurement I got is referring to the end of the case neck to where the rear edge of the mark is worn on the brass. The pictures show the wear marks. So by theory I'd have to trim roughly .060 off a piece of brass to get it to fit in the chamber without hitting.

The brass I used for the pics and measurements were run through a full length sizing die, then seated a bullet.

I agree that the reamer was initially probably run in too far, hence the excessive headspace. Now that the recoil lug has been milled the headspace is correct so that removes the possibility of a deep or shallow chamber.

 

[eschafer]

Guys, forgive me if this is obvious, as it really isn't for me. But how does grinding the recoil lug adjust headspace?.... I know I'm missing something... Thanks..

 

[big5ifty]

Could I use one of the ptg throat reamers to obtain the clearance I need?

My understanding of these things is [ and correct me if I'm wrong ] :

A throat reamer is for the throat, used to extend freebore, not extend the neck portion of the chamber.

A throat reamer can't cut the chamber, and if the chamber neck is too short, the chamber needs to be re-cut.

For the chamber to be re-cut, you don't just shove the reamer into an existing chamber.

The barrel is set back, and a new chamber cut.

Avoid the urge to save money by skimping on anything and trying to make do. With that short chamber neck, if you, or worse - someone else - accidently chamber a regular length loaded round and fire it, the rifle could blow up.

It's close to 100 grains of whatever powder you're using - don't mess with it.

 

[codybrown]

Guys, forgive me if this is obvious, as it really isn't for me. But how does grinding the recoil lug adjust headspace?.... I know I'm missing something... Thanks..

It sets the barrel back further into the action.

 

[codybrown]

How is chamber length measured? My understanding is that it's done off the shoulder like headspace? I may be missing something (very good possibility) but if headspace is correct isn't the chamber correct?

 

[TTE]

How is chamber length measured?

https://www.brownells.com/reloading/measuring-tools/case-length-gauges/sinclair-chamber-length-gage/

 

[Chilly807]

Guys, forgive me if this is obvious, as it really isn't for me. But how does grinding the recoil lug adjust headspace?.... I know I'm missing something... Thanks..

You're not the only one with raised eyebrows. I'm having trouble with that myself. Glad you asked first though.

 

[M-61]

It sets the barrel back further into the action.

Totally lost on this. Turning the barrel is what sets the barrel further into the action. To me, if you throw the recoil lug in the garbage the headspace remains whatever you have set it by turning the barrel in or out of the action. Moving the chamber ( datum line) closer to the bolt face or further away is your adjustment method.
What am I missing here?

 

[SKWERLZ]

Could I use one of the ptg throat reamers to obtain the clearance I need? Even with the clearance issue the rifle will shoot .75 moa with a load worked up for a different rifle so I don't believe the chamber isn't cut fairly straight.

If it is truly the neck a neck reamer would make short work of it.
It’s a different reamer than a throat reamer

They make throat, neck and throat/neck reamers.

I personally would rent a neck and throat reamer and set them individually.

Most 300 rums have a short freebore so you could possibly use a combination neck/throat if the geometry is close.

You can actually get a decent idea of neck length with a depth gauge and really even a set of calipers.
Could be a worn reamer with a tapered or short neck.

 

[DShortt]

Totally lost on this. Turning the barrel is what sets the barrel further into the action. To me, if you throw the recoil lug in the garbage the headspace remains whatever you have set it by turning the barrel in or out of the action. Moving the chamber ( datum line) closer to the bolt face or further away is your adjustment method.
What am I missing here?

On the action being discussed, the recoil lug seats tight against the action face and the barrel shoulder seats tight on the other side of the recoil lug. There is no barrel nut.
So by increasing or decreasing the thickness of the recoil lug you will increase or decrease the headspace measurement. In this particular case the barrel can turn further into the action due to the the thinner recoil lug and thus decrease the headspace.

 

[SKWERLZ]

On the action being discussed, the recoil lug seats tight against the action face and the barrel shoulder seats tight on the other side of the recoil lug. There is no barrel nut.
So by increasing or decreasing the thickness of the recoil lug you will increase or decrease the headspace measurement.

It will also change your boltface/extractor to barrel clearance so you must account for that as well if the barrel is timed upwards

 

[DShortt]

If it is truly the neck a neck reamer would make short work of it.
It’s a different reamer than a throat reamer

They make throat, neck and throat/neck reamers.

I personally would rent a neck and throat reamer and set them individually.

Most 300 rums have a short freebore so you could possibly use a combination neck/throat if the geometry is close.

You can actually get a decent idea of neck length with a depth gauge and really even a set of calipers.
Could be a worn reamer with a tapered or short neck.

That's assuming a throating issue won't appear next.

As others have said the best way to fix this is have a competent person completely rechamber the barrel. Evidently whomever worked on it before didn't know what to look for so no telling what is out of spec.

Then you get to find out if the barrel even shoots accurately.

 

[SKWERLZ]

I can tell you my 300 rum reamer has about .336 of neck length

 

[SKWERLZ]

That's assuming a throating issue won't appear next.

As others have said the best way to fix this is have a competent person completely rechamber the barrel. Evidently whomever worked on it before didn't know what to look for so no telling what is out of spec.

Then you get to find out if the barrel even shoots accurately.

Hence why I recommended also getting a throat reamer.

If your remotely competent and careful doing both is a simple operation.