match chamber or not?

[Idaho Hunter]

I am having a 300 RUM built by my gunsmith and he asked me if I wanted a match chamber or a standard chamber cut into my rifle. The rifle is going to be a dedicated hunting rifle, But I'm not sure what one do go with. I have never had a rifle built before and have only shot stock or semistock rifles.

Any info would be appreciated

Thanks
Chris

 

[Franklin]

I'm not sure exactly what he means by that. Usually smiths ask if you want a standard chamber or one with a tight neck. With a tight neck the smith will let you know what he cut it too and then you have to turn the necks on your brass to chamber them. If your going to use a bushing style die to form your cases then this is a good thing as you need all your brass necks to be the same thickness to use this die to it's full extent. In a hunting gun it's not necessary and you can have a great shooting rifle, but a tight neck can give a little more accuracy at the expense of more brass prep.

 

[BountyHunter]

Could be one of two things

1. Chamber that is just min SAAMI specs that will still fit factory ammo

2. Could be min SAAMI with tight neck. Chances are you do not want this for a pure hunting gun. Factory ammo will not fit.

You need him to clarify what he is talking about.

BH

 

[trueblue]

I think it would be #`1 on BH's list, but you better make sure or you will be turning necks. A match chamber that gives you .004 over loaded diameter of neck is fine for a precision hunting rifle.

 

[Idaho Hunter]

Thanks for all the info, It helped. I'll talk to my gunsmith today and see what he has to say.

 

[Michael Eichele]

I have 2 'match' chambers. Neither of them require any neck turning. They are very snug. This allows for the brass to expand VERY LITTLE. This will do 2 things.

1: It will allow your brass MUCH longer life.

2: Pressure will be higher. This will cause you to have to use reduced handloads to get safe pressures. This doesnt meen that you cant run max velocity potential, just that it will take less powder to get there.

That said, you may not be able to use factory ammo in a 'match' chamber with a short throat even though they will fit as the pressures can be too high. If you want to run factory ammo, you will need a full SAMMI spec chamber AND a decent amount of freebore. If you only want to hand load, the tighter chamber and short throat may be the best option. However, I would also have you follow the other posts advice and double check with your smith about just exactly what he meens. Unless you are building a bech gun, you do not need a tight neck chamber. When it comes to accuracy, tight necks are HIGHLY over-rated in the first place.

 

[BountyHunter]

I

2: Pressure will be higher. This will cause you to have to use reduced handloads to get safe pressures. This doesnt meen that you cant run max velocity potential, just that it will take less powder to get there.

That said, you may not be able to use factory ammo in a 'match' chamber with a short throat even though they will fit as the pressures can be too high. If you want to run factory ammo, you will need a full SAMMI spec chamber AND a decent amount of freebore. If you only want to hand load, the tighter chamber and short throat may be the best option. However, I would also have you follow the other posts advice and double check with your smith about just exactly what he meens. Unless you are building a bech gun, you do not need a tight neck chamber. When it comes to accuracy, tight necks are HIGHLY over-rated in the first place.

Michael

1. First I ever heard of having to reduce powder due to min SAAMI chamber and I have or had 15-20+ of them, reamers to go with most. Most will go over what is listed as max powder to and safely. That is what most "match" chambers are unless they are also tight neck, which has nothing to do with the body dimensions and length of throat.

Plus I have never seen anything ever written about that. Where did you find that at?

2. If any chamber has a short throat, it may not load some factory brass and that means you are jamming way into the lands and have hard closing. that is a given problem with any chamber. However, if you have a chamber like that it is poorly designed period and has nothing to do with min SAAMI.

Reamer mftrs will make any reamer you want, but they all are very capable of putting out "standard" minimum SAAMI chambers that will fit any normal factory round and not cause high pressures. When you call and talk to them, that is the type they will normally recommend unless you are an experienced wildcatter and want something out of the ordinary. They will do that too.

They will also discuss the type and weight of bullet you want to match the freebore. A reamer built specifically for a 30 cal 125 Btip touching the lands will not even chamber a 210 VLD.

Sounds like someone gave you slightly short throated chambers if you are running into that issue and that is another problem on its own.

BH

 

[Michael Eichele]

Of the 3 tight chamber barrels I have had (currently have 2) utilizing minimal freebore, all have generated excessive pressures. For example, my current 308 has a tight chamber (tight meaning a factory case will fit but there is no room for much if any real expansion) and has a throat short enough to seat AMAX's to the lands at near SAAMI OACL depths. Shooting factory Federal GMM 168 SMK's, they run at just under 2800 FPS. Published is 2600 FPS. The previous 308 I had utilized a slightly larger chamber and lots of freebore. The same loads ran just over 2600 FPS. The 300 RUM's I was using showed the exact same thing EXCEPT with 100 grains of powder, the pressures were much more dramatically high. In short I have NEVER been able to get close to factory published charge weights in any of my custom barrels and maintain normal velocity levels. I have reached normal velocities and even higher than normal velocities. Just never with published charge weights. For example, published charge weights for the 300 RUM are about 100 grains of RETUMBO using a 180 class bullet in the 300 RUM. Published velocity is around 3300 FPS. For me to get 3300 FPS in both my RUMs took 90 grains of powder. 100 grains would have posed a serious problem. I made the mistake of starting with 95 grains and destroyed my extractor on the very first shot. I am shocked that in all the custom barrels you say you have had that you have never experienced this.

My opinion is that when a case has no room to expand and the bullet engages the lands sooner than later, high pressures WILL result. Offer the case a bit of room to expand and the bullet to get a running start and the pressures fall. Hence my comments about using factory ammo in a custom stick with tight tolerences.

Take it or leave it, these are my experiences with 'match' chambers and short throats. Short meaning getting the bullets to engage the lands and have them near standard OACL.

If I were the only guy I knew of that had experienced this (or if all the rifles came from the same smith) I wouldnt neccesarily take it at face value. I know of plenty of other caces that this has happened. I know one case where he was using a snug chamber and minimal freebore. When he shot one round down the pipe using factory 300 WSM loads, the smith had to turn the barrel off of the action to get the case releived so it could be removed. I guess what I am saying is that if you want to shoot factory ammo in a custom stick, pay attention to chammber and throat demensions. Just because factory ammo will fit and fit smoothly, doesnt meen that it will be safe.

 

[MontanaRifleman]

The 300 RUM's I was using showed the exact same thing EXCEPT with 100 grains of powder, the pressures were much more dramatically high. In short I have NEVER been able to get close to factory published charge weights in any of my custom barrels and maintain normal velocity levels. I have reached normal velocities and even higher than normal velocities. Just never with published charge weights. For example, published charge weights for the 300 RUM are about 100 grains of RETUMBO using a 180 class bullet in the 300 RUM. Published velocity is around 3300 FPS. For me to get 3300 FPS in both my RUMs took 90 grains of powder. 100 grains would have posed a serious problem. I made the mistake of starting with 95 grains and destroyed my extractor on the very first shot.

Interesting... In my factory Sendero 300 RUM, which has a long throat, 180 E-Tips max out at 97.5 gr of Retumbo @ 3400 fps.

When you blew your extractor, what happened to the case? Did it remain intact? And what type of extractor was it?

-Mark

 

[Michael Eichele]

Interesting... In my factory Sendero 300 RUM, which has a long throat, 180 E-Tips max out at 97.5 gr of Retumbo @ 3400 fps.

When you blew your extractor, what happened to the case? Did it remain intact? And what type of extractor was it?

-Mark

You should expect a solid copper bullet with more bearing surface to generate more pressure than a softer jacketed lead bullet with less bearing surface. This is why the original barnes loading manuals always had lower charges for average velocities. You simply could not use standard loading data. The grooves they use now eliminate this issue. That is why you are seeing higher than average velocity with less than published charge weights. If you used the 180 Ballistic tip or better yet the thinner jacketed and shorter 178 AMAX and your charge of 97.5, I bet you would see a noticable drop in velocity.

The extractor was factory. It pulled apart while trying to extract the case. The case was able to be tapped out with a cleaning rod and shortly after that my bolt was sporting a sako style extractor.

 

[BountyHunter]

Interesting, mine and most other LR BR guys are seeing the opposite. We normally are into the lands and loads over book in many if not most cases.

Now I have seen one gun that was built with an absolutely too tight chamber and it had to be rechambered simply because no factory dies were tight enough to resize them after 3 loadings.

BH

 

[MontanaRifleman]

You should expect a solid copper bullet with more bearing surface to generate more pressure than a softer jacketed lead bullet with less bearing surface. This is why the original barnes loading manuals always had lower charges for average velocities. You simply could not use standard loading data. The grooves they use now eliminate this issue. That is why you are seeing higher than average velocity with less than published charge weights. If you used the 180 Ballistic tip or better yet the thinner jacketed and shorter 178 AMAX and your charge of 97.5, I bet you would see a noticable drop in velocity.

The extractor was factory. It pulled apart while trying to extract the case. The case was able to be tapped out with a cleaning rod and shortly after that my bolt was sporting a sako style extractor.

I have heard that about the E-Tips, but haven't seen a lot of evidnce of it in my rifles.

There has been a big heated debate in the AOD shooting forum over the Rem vs Sako extractor issue, so that's why I asked.

-Mark

 

[Mike 338]

Sooo, just curious,

What type of chambers are used by custom makers that have accuracy guarantees? Will a match chamber do all that much to shrink groups?

 

[Bart B]

I don't think one need a "tight" match chamber of any flavor. Standard SAAMI spec ones have been winning matches and setting records since they've been around. Sierra Bullets' been using SAAMI spec (or virtual versions thereof) since the 1950's testing their stuff for accuracy. I doubt anybody shoots 'em more accurate than they do. And they've been full length sizing their test cases since then, too.

Once one understands how a rimless bottleneck case fits the chamber when it fires, they will understand why "tight" match versions don't center those cases with custom turned necks any better than SAAMI spec ones with the same custom turned necks to align the bullet very well with the bore. The requirement that a tight chamber neck is needed for best bullet alignment with the bore's with rimless bottleneck cases is another myth.