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Discussion Starter · #1 ·
I just built my first AR-10 platform and chose the 375 Raptor. I've built over a dozen 15 platforms and finally wanted to delve into the larger frame and figured I'd try something unique to get my feet wet.. I'm running into a problem that I've never encountered before. I've searched the net, spoken to people, etc, and thus far haven't found anyone else who has experienced my problem. I'm asking questions on any forum I can find people who have a 375 Raptor of their own.

Anyway, initially I simply loaded some dummy rounds to test chambering, etc, using the load data found on the 375raptor.com website. Specifically I was using the Speer 270 grain SPBT bullets and the Barnes 235 grain TSX. When I loaded the Speers to the specified length the bullets were getting stuck in the lands. After a bit I realized my seating die was hitting the tip, not the ogive, and was deforming it so I was getting a bad reading. However, by that point I had contacted X-Caliber and they said they wanted the barrel back to check the chamber because when they measured their reamer it seemed off spec. In the meantime I acquired a Hornady OAL gauge and comparator so I could get some dummy rounds loaded which matched the barrel....I put the Speer .020 off the lands and the Barnes .045 off as per their recommendation....and sent the dummy rounds off with the barrel.

So now for the problem. Steve at X-Caliber emailed me and stated everything in the chamber measured out exactly to spec and that the dummy rounds I loaded were seated too long for the freebore. Here's what he wrote, "After looking at your dummy loads, and while they do meet COAL requirements, the bullet's max-diameter protrusion (the widest portion of the bullet which protrudes past the case mouth) run rather long, longer than the 0.150" length limit the freebore allows. The bullets will have to be seated deeper to accommodate this measurement." I seated them based on the actual ogive to lands fit as per the measurement I got from the OAL gauge and comparator measurement. They both chamber just fine and eject without a problem. Does anyone here load their own and if so did you have any issues similar to this? Anyone think I did something wrong and really need to go shorter or might there be another explanation?

Any advice or suggestions?

TIA
 

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Weatherlite, I've read your write-up 4 times and do not understand what your problem is. You got your barrel back and you stated

"I seated them based on the actual ogive to lands fit as per the measurement I got from the OAL gauge and comparator measurement. They both chamber just fine and eject without a problem. "

I'd like to comment but, what is the problem? You gave no details on what COALs or base to ogive and how much deeper you think you have to seat your bullets. Is the problem only occurring when you load and try to fire a live round (powder in the case)?
 

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Discussion Starter · #3 ·
I apologize....sometimes when I read it back it makes sense to me even though I've left out certain details. I'm a dork. Lol

So I actually haven't fired anything through the barrel yet. The dummy rounds chambered just fine before I sent it off. They still do. I'm just concerned because when the manufacturer of a barrel tells you your loads are too long you would assume that's a big problem. However, he didn't tell me how much deeper they should be seated either, so I don't know if it's actually that bad.

To give you specifics, the Speer is loaded to an ogive length of 2.104 which is .020 off the lands, and has a COAL of 2.771. The recommended COAL is 2.790. As for the Barnes, ogive length is 2.0825 which is .045 off the lands, for a COAL of 2.663. That is .003 longer than the recommended 2.660, but well under the max of 2.800 for the magazine and a reasonable tolerance for a non-micrometer seating die.

I understand that some bullets can be seated quite a bit off the lands. In fact my 458 SOCOM has one load which is almost a quarter inch off the lands, but it also falls within a reasonable amount of play from the recommended COAL. These two for my 375 are seated where one would think they should be, but the manufacturer says to go deeper. I guess the question is just how much further should I go? I would imagine I could go .125 off the lands and work my way in closer while checking the brass as I go, but since I've never been told my load is messed up I've never had to experiment in this way before and am seeking advice on how to proceed.

Hopefully that makes more sense?
 

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Weatherlite, thanks for the extra details. This doesn't sound like a cartridge specific issue; it could be for any cartridge. In fact, I don't see that you have a specific problem if your dummy loads are cycling without issue.

Here are some comments to consider. I start my Barnes bullet loads at 0.050" off the lands but will work them into 0.035" off the land when adjusting COAL to fine-tune for smaller group size. These copper bullets are hard enough that the bullet seating die shouldn't alter bullet shape. So long as your load development isn't starting near published max, I don't see where this load would have any issues.

The Speer lead-core may need more attention. Unless they are match-grade bullets, I often find ogive variation with lead-core bullets that can cause cartridge base to ogive variation where 0.020" off the lands may not provide enough margin when the bullet seater is touching close to the bullet's tip. I like to start loading match bullets 0.010" of the lands but with general lead-core hunting bullets, I often load a COAL where the cartridge base to ogive measurement is never longer than 0.020" off the lands (measuring 10 rounds as a sample size). Its not fun being in the field and trying to extract a round that has engaged the lands. The comment of not starting loads near max applies.

If I achieve moa or better with my initial distance to the lands with hunting load development, I'm satisfied and start learning how the rifle does at different ranges. If I would like to tighten up the group size, I test COAL in 0.015" increments. Adjusting COAL can be a powerful level for shrinking crop size.

Enjoy your Raptor!
 

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This is an issue with various .223 bullets I shoot in in service rifle matches. The 77gr bullets can be loaded to the full 2.260 COAL, but some 69s have to be loaded shorter because the bullets ogive is fatter and will contact the lands if you try to load them to 2.260. It is bullet dependent. The nose of bullets always stick down the bore past the leade. So some bullets have to be loaded shorter than the cartridge max COAL due to bullet ogive design and length.
 

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I appreciate the extra info and insight. If I come to a working and repeatable solution to this I will update the thread. Thanks!
I had the same problem when loading dummies for my new 375 Raptor for different bullets and trying to use net picked info for the max. COL:s for different bullets. The leade/freebore was just too short for some bullets when 'official' suitable COL's used for the dummies. Don't know the reamer used or manufacturer who did it, but the leade was too short and solution for it was easy. I told to my smith that I need certain amount of more freebore for some bullets to max the cartridge length to fit perfectly my mags, and he reamed a bit more freebore to the chamber with maybe a separate throat reamer usually used for making 375 H&H rifles. Because a wildcat, there may be variation in reamers and in my case the chamber reamer did initially a bit too short throat for some bullets. Could happen to commercial barrel makers also, not only for a single gunsmith.
 

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I have an X-Caliber 375 Raptor barrel that was finished this summer. I seat the 270gr Speers To around 2.790”, feeds and shoots great. Those lead tips vary quite a bit, so I seated bullet to jam then went 20thou deeper. Ensured it hand cycled reliably and fit into magazines. I have not moved my seating die depth since. Going further from lands wouldn't hurt any, but I would be cutting into case capacity at that point.
 

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Discussion Starter · #9 ·
I've been reaching out everywhere and eventually I was put in touch with the creator, Arne Brennan. To sum up what I've gleaned from all these various conversations, combined with the wisdom of the man himself, there are several points to make....which are probably obvious to some but since this is my first foray into a wildcat it was for me.

First, Arne couldn't divulge the chamber measurements but he confirmed the .150 straight freebore and added there is also an additional tapered throat with a 3.5 degree angle....and a length he couldn't reveal. This means when using the OAL tool it's really easy to mess up and have two vastly different measurements. At the transition from straight to tapered you'll meet resistance which usually means that's the beginning of the lands. That should be recorded as ogive length 1. With ever so slightly more pressure the bullet slides down the tapered throat and meets the actual lands. That is ogive length 2. Some bullets might not hit the first bit of resistance and may only have the single deeper one.

Next, the distance you come up with for an ogive length will be different depending on what type of bullet you use because of how quickly the ogive tapers up to the full diameter. This might be confusing at first but still write it down and find the two distances as stated above.

For safety use that first, shortest, distance for the ogive length with a lowish starting powder load. Next work your way in checking for signs of pressure on the way until you either see a change or reach the deeper measurement. If you reach the deeper level move up the load and start back at the first measurement and repeat. If you get signs of pressure before then you can proceed with figuring out best load/distance with a shorter distance. Of course, this will have to be repeated for each bullet. According to Arne pressure can be vastly different at the same depth/powder load with different bullets. And with the fact two different barrels might have two different measurements the loads he developed (found on the Raptor home page) are guides only....just like all other loads found on the web. Lol

Basically it sucks and will take a lot of rounds, but it will be best in the end.

Hopefully this all made sense.
 
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