Custom rifle with short freebore

[pineywoods]

Had a Remington 700 re-barreled with a Hart chambered to 25-06. The gun shoots handloads great but won't chamber some factory loads- particularly bullets with a short bearing surface. Apparently the chamber dimensions are fine but the freebore is .035 whereas SAAMI is .104. The gunsmith used a match reamer- I'm assuming this reamer was designed to shoot VLD type bullets & extend throat erosion life. The gun will routinely shoot under .5 MOA with anything I've worked up in it so I'm hesitant to "fix" it. However, this is a hunting rifle & I'm generally shooting 115 & 117 gr bullets which have to be seated .069 deeper than normal- somewhat intruding on powder space & I would think negatively affecting pressure. Is the short throat a benefit or a handicap in your minds?

 

[J E Custom]

Had a Remington 700 re-barreled with a Hart chambered to 25-06. The gun shoots handloads great but won't chamber some factory loads- particularly bullets with a short bearing surface. Apparently the chamber dimensions are fine but the freebore is .035 whereas SAAMI is .104. The gunsmith used a match reamer- I'm assuming this reamer was designed to shoot VLD type bullets & extend throat erosion life. The gun will routinely shoot under .5 MOA with anything I've worked up in it so I'm hesitant to "fix" it. However, this is a hunting rifle & I'm generally shooting 115 & 117 gr bullets which have to be seated .069 deeper than normal- somewhat intruding on powder space & I would think negatively affecting pressure. Is the short throat a benefit or a handicap in your minds?

SAMME chambers are designed to handle all types of bullets If loaded to SAMME mag lengths.

Changes in these dimensions can bring problems with them, Like the short Freebore. Normally this is done because someone wants to shoot a certain bullet only. The downside of these alterations is If the rifle doesn't like that Bullet you are stuck with no where to go.

There is no such thing as a Match reamer. There are SAMME reamers and there are Non SAMME reamers (Dimensional changes) and the reamer will be marked identifying the changes. also calling a reamer a match reamer does not make the chamber better than a SAMME chamber if the chamber is cut to close tolerances, only different.

A good smith can throat it to SAMME specs. without altering the rest of the chamber allowing you to shoot any bullet you want. And yes, short freebore can drive pressure up prematurely.

J E CUSTOM

 

[pineywoods]

Thanks for your input JE. I started to take the rifle back once I realized a couple of factory rounds wouldn't chamber. Once I fire formed some cases & saw how accurate the gun was along with the fact that I handload exclusively.... I reconsidered. I'm thinking .069 difference is negligible ? & may buy me some barrel life. The only problems I can see come in are if larger bullets need to be backed away from the lands & I'm shooting a case full of slow burning powder. I haven't loaded anything slower than IMR 4831 which has proven extremely accurate with 100 ttsx & 117 sst (The new IMR 4451 is giving similar results). If my assumption on the freebore being negligible is wrong I'd love to hear some more feedback.

 

[J E Custom]

Thanks for your input JE. I started to take the rifle back once I realized a couple of factory rounds wouldn't chamber. Once I fire formed some cases & saw how accurate the gun was along with the fact that I handload exclusively.... I reconsidered. I'm thinking .069 difference is negligible ? & may buy me some barrel life. The only problems I can see come in are if larger bullets need to be backed away from the lands & I'm shooting a case full of slow burning powder. I haven't loaded anything slower than IMR 4831 which has proven extremely accurate with 100 ttsx & 117 sst (The new IMR 4451 is giving similar results). If my assumption on the freebore being negligible is wrong I'd love to hear some more feedback.

In my opinion, Freebore is very important to control Pressure, Especially on the large over bored
cartridges. It allows the bullet to start moving before it impacts the rifling reducing the initial pressure spike and aids the bullet in the engraving of the rifling.

If you look at the SAMME specifications, You will see that most high pressure, high velocity cartridges have quite a bit of free bore for this reason.

Seating the bullet against the lands increases the pressure and reduces the velocity. The best example I have seen is in the case of a friend building a 30/378 with less than .100 thousandths
freebore. After blowing nearly every primer in factory Weatherby ammo He had to load down to prevent this and lost over 100 ft/sec in velocity. Weatherby ammo used to be loaded to the max
(Roy Weatherby wanted velocity so his claims of the fastest were true) with the shore freebore pressures were just to high, So In reality, the reason for the 30/378 was velocity, the effect was no more velocity than the 300 RUM.

J E CUSTOM

 

[pineywoods]

I need to get a chronograph & check velocities...period. I'm still a bit confused about the freebore thing though. The distance a bullet is from the lands is a given- regardless of freebore. With the exception of Barnes & Berger bullets, Most folks are seating .010 to .015 off the lands or touching. Are you saying overbore calibers benefit from more bullet jump with a longer throat? It would seem next to impossible to get a bullet touching the lands in a rifle with more freebore. This almost seems like an advantage in my rifle, particularly with 85 to 100 gr bullets. Isn't pressure correlated to bullet distance from lands ? How does freebore play into ?I'm probably confused....
Basically, if I keep the rifle as is, the worst thing that can happen is a slight loss of velocity. I really hate to mess with a gun that shoots so well. I'll assume reaming the throat out for more freebore could cause an accuracy issue if not done absolutely correct.

 

[J E Custom]

I need to get a chronograph & check velocities...period. I'm still a bit confused about the freebore thing though. The distance a bullet is from the lands is a given- regardless of freebore. With the exception of Barnes & Berger bullets, Most folks are seating .010 to .015 off the lands or touching. Are you saying overbore calibers benefit from more bullet jump with a longer throat? It would seem next to impossible to get a bullet touching the lands in a rifle with more freebore. This almost seems like an advantage in my rifle, particularly with 85 to 100 gr bullets. Isn't pressure correlated to bullet distance from lands ? How does freebore play into ?I'm probably confused....
Basically, if I keep the rifle as is, the worst thing that can happen is a slight loss of velocity. I really hate to mess with a gun that shoots so well. I'll assume reaming the throat out for more freebore could cause an accuracy issue if not done absolutely correct.

If you load to magazine length minus .010 to .020 the SAMME dimensions will give you plenty of freebore. If you shoot close or touching the lands you may have to single load.

It is assumed that seating close or against the lands improves accuracy, IT does Not. some bullets
shoot better .020 off the lands and others shoot there best at or over .100 thousandths off the lands.

I have seen bullets like the Bergers perform from .000 to .120 of the lands. The only time that it may be an advantage to jam the bullet against the lands is if you are shooting poor quality ammo (Factory or re loaded) or a poor quality chamber that is not concentric.

With a good concentric chamber and concentric and properly sized ammo it is not necessary for the bullet to touch the lands to be centered.

The bottom line is that anything that is done poorly effects accuracy.

Weatherbys are known for there velocity and they all have generous freebore (.361 to .373) on all but the 378 and 460 that have .756 For the use of round nose bullets.

I own 4 rifles that will all shoot under .100 5 shot groups and one of them is a 30/378 with a .361 freebore and consistently shoots less than .100 (1/10th of a MOA) I also load everthing to mag length minus .010 to .020,

So if it shoots good and you are happy with accuracy, Don't touch it. Just watch for signs of pressure.

J E CUSTOM

 

[pineywoods]

JE....thank you sir for your insight & time. Folks like you are much appreciated in my world. You've definitely managed to clear some things up for me & if you are ever around Lufkin I'll gladly get lunch.

 

[J E Custom]

JE....thank you sir for your insight & time. Folks like you are much appreciated in my world. You've definitely managed to clear some things up for me & if you are ever around Lufkin I'll gladly get lunch.

Thank you, for a very gracious offer.

Be careful what you ask for, Ha Ha.

J E CUSTOM

 

[Rich Coyle]

I am going to post something that used to really gal my brother when we were in business together. "I fail to see the problem." Another thing I'm thinking is, "If it ain't broke, don't fix it." You're a loader, load for it.

 

[pineywoods]

I am going to post something that used to really gal my brother when we were in business together. "I fail to see the problem." Another thing I'm thinking is, "If it ain't broke, don't fix it." You're a loader, load for it.

A loader that needs a chronograph !

 

[Rich Coyle]

A loader that needs a chronograph !

How many years did we old geezers load and how many thousands of rounds did we fire without chronographs and without problems? I remember getting my highest velocities with duplex loads until some of the more modern powders came out.

 

[pineywoods]

As a novice, I'm a scaredy cat...never exceeded a max book load with anything but my 6.5 swede. I've read what to look for as far as excess pressure signs but haven't seen any yet. I figure a chrono will be a good tool that will perhaps speed my learning curve. I also ordered a magnifying lens to examine my cases more closely.