Long Range Hunting Online Magazine


Go Back   Long Range Hunting Online Magazine > Rifles, Reloading, Optics, Equipment > Rifles, Bullets, Barrels and Ballistics


Reply

match chamber or not?

 
LinkBack Thread Tools Display Modes
  #8  
Old 02-24-2010, 03:47 PM
Platinum Member
 
Join Date: Jan 2003
Location: The rifle range, or archery range or behind the computer in Alaska
Posts: 3,514
Re: match chamber or not?

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.
__________________
Long range shooting is a process that ends with a result. Once you start to focus on the result (where the shot goes, how big the group is, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.

Last edited by Michael Eichele; 02-24-2010 at 04:08 PM.
Reply With Quote
  #9  
Old 02-24-2010, 04:04 PM
Platinum Member
 
Join Date: May 2008
Location: South of Canada and North of Wyoming
Posts: 5,954
Re: match chamber or not?

Quote:
Quote:
Originally Posted by Michael Eichele View Post
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
Reply With Quote
  #10  
Old 02-24-2010, 04:16 PM
Platinum Member
 
Join Date: Jan 2003
Location: The rifle range, or archery range or behind the computer in Alaska
Posts: 3,514
Re: match chamber or not?

Quote:
Originally Posted by MontanaRifleman View Post
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.
__________________
Long range shooting is a process that ends with a result. Once you start to focus on the result (where the shot goes, how big the group is, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.

Last edited by Michael Eichele; 02-24-2010 at 04:28 PM.
Reply With Quote
  #11  
Old 02-24-2010, 06:28 PM
Platinum Member
 
Join Date: Jun 2007
Location: Fredericksburg VA
Posts: 4,118
Re: match chamber or not?

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
Reply With Quote
  #12  
Old 02-24-2010, 08:28 PM
Platinum Member
 
Join Date: May 2008
Location: South of Canada and North of Wyoming
Posts: 5,954
Re: match chamber or not?

Quote:
Quote:
Originally Posted by Michael Eichele View Post
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
Reply With Quote
  #13  
Old 06-05-2012, 10:37 AM
Gold Member
 
Join Date: Feb 2012
Location: Boise, ID
Posts: 695
Re: match chamber or not?

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?
Reply With Quote
  #14  
Old 06-05-2012, 07:34 PM
Platinum Member
 
Join Date: Dec 2005
Posts: 2,114
Re: match chamber or not?

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.
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes


Similar Threads for: match chamber or not?
Thread Thread Starter Forum Replies Last Post
Federal Gold Medal Match 175gr Sierra Match King Southernfryedyankee Rifles, Bullets, Barrels and Ballistics 4 11-24-2011 12:27 PM
?Match Chamber? kc Gunsmithing 1 01-08-2011 04:28 PM
F/S or WTT winchester 53 gr match bullets (2253h match) foxhunter Reloading Equipment and Components 1 05-02-2010 01:54 PM
50bmg,Match chamber thocon Equipment Discussions 1 12-03-2004 06:30 PM
match kings,A-max ,Palma match for game?? Jonathan Long Range Hunting & Shooting 5 09-14-2001 10:10 AM

Current Poll
In the last 12 months, what was your longest rifle kill on big game?
0 to 200 yards - 26.00%
1,546 Vote
201 to 400 yards - 32.16%
1,912 Vote
401 to 600 yards - 23.02%
1,369 Vote
601 to 800 yards - 10.02%
596 Votes
801 to 1,000 yards - 3.90%
232 Votes
Over 1,000 yards - 4.89%
291 Votes
Total Votes: 5,946
You may not vote on this poll.

All times are GMT -5. The time now is 05:29 AM.


Powered by vBulletin ©2000 - 2014, Jelsoft Enterprises Ltd.
Content Management Powered by vBadvanced CMPS
All content ©2010-2014 Long Range Hunting, LLC