6.5 Creedmoor .125 freebore

[Crews]

I recently attained a custom rifle in 6.5 Creedmoor. The barrel is a 21" light Palma, with an 8 twist. I was told that the chamber was cut with a .125 freebore. I'm not a reloader and don't really understand freebore, but was told to stick with the 120's. I was also told that as a general rule of thumb, it was safe to shoot it as long as the ammo didn't jam in and make the bolt hard to close. Or pull the bullet out when extracting. Makes sense to me.

I went to the range and tried out some box ammo over the Magnetospeed. Hornady 120 A-Max, Hornady 120 ELD-M, and FGMM 130 Berger Hybrids. The 120 A-Max did great, outstanding accuracy and a SD in the low teens. The FGMM 130 Bergers also did well on paper, but the SD was really high... in the upper 20's or low 30's (forgot my notes at home.) Finally, I didn't have time to chrono the 120 ELD-M's but I felt a TINY bit of resistance when closing the bolt. I dunno, maybe just me being paranoid.

Here are my questions, hopefully ya'll can help this ignorant guy with some advice:

1. I expected better consistency with the FGMM. Is there any chance the velocity variance came from the 130 Berger Hybrid not playing well with my chamber?

2. Is there enough difference between the 120 A-Max and the 120 ELD-M to cause any issues with my chamber? I'd love to just stick with shooting the 120 A-Max indefinitely, but I'm worried that the supply will dry up at some point.

I'd like to have enough options available that I can continue shooting this barrel until I wear it out, and not spend extra $ re-cutting the chamber. Obviously, I will get a normal chamber on the next one.

 

[Rob01]

Don't plan on using the 120 AMAX for the whole barrel unless you can find a place that has 2500-3000 of them for sale as they have been discontinued. The 120 ELD is slightly different but not enough to worry about in a normal chamber but with the super tight freebore you have, SAAMI freebore is .199 for comparison, I would just check it to make sure it isn't jammed super deep although if it shoots and no pressure a slight jam won't hurt anything either. Chamber one and pull it out and see if you have any movement in seating depth or marks on the bullet. Did you see any pressure in the 120 ELDs you shot?

 

[vh20]

Using a factory-loaded round, color the entire ELD-M 120 bullet with a black Sharpie, gently place it in the chamber, close the bolt, and carefully extract it without scratching the bullet. Any contact with the rifling will be pretty easy to see.

 

[Crews]

Did you see any pressure in the 120 ELDs you shot?

the bolt lift on extraction didn't seem any heavier. I did see some minor marks on the bullet when I pulled one live round out, but it could have been from feeding out of the mag. I did keep the brass, perhaps I google pressure signs on brass and inspect them. I will also go home and do that sharpie trick and see what it looks like.

 

[spife7980]

I did keep the brass, perhaps I google pressure signs on brass and inspect them.

Brought to you by forum member Orkan
https://www.primalrights.com/library...nding-pressure

 

[Crews]

excellent resource, thanks for the link!

 

[Sig Marine]

You don't have to re-cut the entire chamber, just have a gunsmith hit it with a throating reamer to the length you want. I know Robert at RW Synder Gunsmithing charges about $50 to push the throat out. Here's a link to his site: https://www.rwsgunsmithing.com/

 

[Crews]

Oh okay, that’s great news... doesn’t sound like it would take an act of congress to fix.

 

[spife7980]

Oh okay, that’s great news... doesn’t sound like it would take an act of congress to fix.

Nope, one of the easier fixes.

Im not advocating you do this yourself (I would still go through a smith myself) but they make kits to do it by hand even just to show that it isnt the end of the world http://pacifictoolandgauge.com/throa...oater-kit.html
[IMG2=JSON]{"data-align":"none","data-size":"full","src":"http:\/\/pacifictoolandgauge.com\/3904-large_default\/17-cal-uni-throater-kit.jpg"}[/IMG2]

 

[Crews]

So I had some FGMM and 120 ELD left over. Colored them both with a sharpie and chambered them. The FGMM is very easy to close the bolt on, and extraction is smooth with no resistance. The 120 ELD has a very slight resistance when I close the bolt, and a very slight resistance when I extract. Only when going slow, nothing that I would really notice much during normal operation.

Spent brass doesnÂ’t show any major signs of overpressure, if any at all.

Does this image tell me anything? The bare spot is in the same place on both bullets, but not all the way around. Would there be marks anywhere else if the bullet was jammed too far into the rifling?

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[Crews]

Magnetospeed results:

120ELD-M
Min 2821 Max 2864; Avg 2842 SD 12.5

FGMM 130 Berger
Min 2782 Max 2872; Avg 2820 SD 25.7

Only a single 10-shot group of each. Perhaps it’s just too small a sample size for me to make any assumptions about the FGMM.




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[spife7980]

You say it’s not all the way around. Is that you inserting it from a mag and scraping the chamber or are you dropping it in straight down the tube gently? Is your ejector removed? Because unlesss you’re cramming it against the walls yourself or the ejectornis doing it for you that looks like you’re at least touching the leads if not .02 in the lands. Whenever I do my lands tests I’m always just off so I only see the several rectangles and not full in jam like that would indicate. I’d say you have a really short throat.

 

[Crews]

I dropped the live rounds in the chamber by hand, with the bolt open. The extractor is still in the bolt though, so maybe that is a mark from pulling them out of the chamber?


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