6.5 PRC Reamer & Seating Depth Considerations
Yesterday I had a good talk with Travis Stevens of TS Customs. He called because he discovered an interesting thing regarding the PRC and wanted to talk it through. Here are the facts.
The original reamer spec that most folks have been using to chamber PRC barrels is likely not going to natively work with the recently launched hornady factory ammo. This came to light due to the recently released Hornady reamer spec which JGS has as of just a few days ago. On that print, the freebore is indicated as .1882". The reamer that Travis presently has matches the spec PT&G had on file for the PRC which puts the freebore at .1302".
I've worked with chambers on that original PT&G reamer as seen here: https://forums.gunhive.com/topic/167...and-ts-customs
You'll notice in that write-up I was using a berger 140 hybrid and ended up ten thousandths off the lands with an OAL of 2.940". Hornady factory ammo is measuring 2.945 for both the 143ELDX and 147ELDM. Based on tip to ogive measurements, this would put hornady factory ammo jammed into the lands on the original PT&G reamer spec about ten thousandths. On the new reamer with the .1882 freebore, you'd be looking at approx 50 thousandths jump. Tip to ogive measurement on a 140 berger hybrid is about 20 thousandths longer than a 147 hornady... so you can plainly see what this differing spec can mean for those looking to shoot factory ammo in their "old" chambers.
Some obvious things about that situation are that if you have an "old" PRC chamber, factory ammo will be jammed... while if you have a "new" PRC chamber, you'll never be able to get closer than 40 thousandths or so from the lands in max strapless AICS format magazines like Accuratemag.
I do not know where the PT&G original spec came from, but it's clear that the hornady spec reamer print from JGS would indicate the future direction of the design and this is further supported by the fact their current factory ammo will certainly work fine in their new spec. It does present a dilemma for handloaders or custom builders however. On one spec you can run a short freebore and be able to approach the lands at mag length. On the other spec you'd never be able to approach the lands in a short action with the longest mags available for it. A mid or long action with associated mags would be the only way to get into the lands with the "new" spec.
Both Travis and I felt it prudent to do a little PSA about this situation, as it's likely there are more than a couple rifles out there with short PRC chambers that will result in factory ammo being jammed to the tune of 10 thousandths or better.
norcal_in_az last edited by
dddoo7 last edited by
Well. This is not the confusion that a new caliber needs in order to take off. I hope it still goes as it seems like a really good caliber to play with.
It will still take off... for certain. It will be "the" big 6.5 in the coming years.
norcal_in_az last edited by
I know this cartridge was designed with target shooting in mind, but how would it be as a hunting round?
ragnarnar last edited by ragnarnar
I’ve wondered, and this seems like the place to ask in light of this discovery: what is the consequence (safety wise) of jamming a round 10 thousandths? What about more, say 30-50 thousandths or even way longer?
I’ve heard of 10 thou jam before so that seems fine. Other than spiking pressure in this case it doesn’t seem to me like it would be dangerous assuming pressure doesn’t go over the limit. In the case of the really long rounds it seems like the lands would push the bullets back into the case to a safe jam length. It seems to me this would be a great way to fireform- just load way way long.
Any jam what so ever and you restrict the bullet's forward momentum. Basically, as the powder expands in the case, you're leaving the "cap" on longer which results in a much more drastic pressure spike. 30 thousandths jam is a HARD jam. You most often can't jam much harder than that because at some point you'll start shoving the bullet back into the case with the lands.
For instance, when fire forming, I'll often have about 30 thousandths of jam. It's generally not easy to close the bolt.
So ten thousandths jam is definitely going to produce more pressure. Likely not enough to cause major problems, all things being equal. ... but sometimes all things are not equal.