COAL - 308 SMK safe seating depths.

W

Wildcard91

Regular
Rating - 100%
14   0   0
I'm currently doing load development and have hit a specific dilemma regarding COAL. Here is what I'm working with.

-Factory Brass once fired out of Savage 10 FCP-K (same rifle being loaded for) 308win - Chamber headspaced to exactly 1.630 from the factory.
-Brass Neck Sized and trimmed, deburred and chamfered to 2.005"
-Brass checked to fit in chamber. Bolt closes easily
-Bullet: 168 Gr. SMK
-COAL seated to 2.800

When cambering a dummy round to these specs the bullet is making contact with the lands and grooves, which is good. However when I extract the round, there are clear and distinct chatter marks from the lands and grooves being left on the round. COAL of the extracted dummy round is now 2.784 and not 2.800. When I load another dummy round to 2.784, the chatter marks are still there with the same width, but are less pronounced.



Question: Based on the picture below, does this suggest that the current COAL is too long for accurate groups and preserving the maximum life of the chamber? Should I start seating my bullets for 2.784" to 2.764" instead of 2.800? Which is likely to be the more accurate round, without having to waste a few loads down range? I'm trying to save the number of trips back and forth from the range. What is the ideal seating depth from the rifling for max accuracy?

Also, the Lee manual states that the min COAL for a 168 jacket bullet is 2.800 with H4895. Is it safe for me to be seating the bullets this far back?

Thanks

DSC_0141.jpg
 
Last edited:
Wildcard91 said:
I'm currently doing load development and have hit a specific dilemma regarding COAL. Here is what I'm working with.

-Factory Brass once fired out of Savage 10 FCP-K (same rifle being loaded for) 308win - Chamber headspaced to exactly 1.630 from the factory.
-Brass Neck Sized and trimmed, deburred and chamfered to 2.005"
-Brass checked to fit in chamber. Bolt closes easily
-Bullet: 168 Gr. SMK
-COAL seated to 2.800

When cambering a dummy round to these specs the bullet is making contact with the lands and grooves, which is good. However when I extract the round, there are clear and distinct chatter marks from the lands and grooves being left on the round. COAL of the extracted dummy round is now 2.784 and not 2.800. When I load another dummy round to 2.784, the chatter marks are still there with the same width, but are less pronounced.



Question: Based on the picture below, does this suggest that the current COAL is too long for accurate groups and preserving the maximum life of the chamber? Should I start seating my bullets for 2.784" to 2.764" instead of 2.800? Which is likely to be the more accurate round, without having to waste a few loads down range? I'm trying to save the number of trips back and forth from the range. What is the ideal seating depth from the rifling for max accuracy?

Also, the Lee manual states that the min COAL for a 168 jacket bullet is 2.800 with H4895. Is it safe for me to be seating the bullets this far back?

Thanks

DSC_0141.jpg
Click to expand...


different gun obviously, but in my rem 700 in 308 i run 165SMK at COAL 2.750 with sub MOA results
 
my under standing is that the sammi 2.800 was an overall length max given to make sure that all military ammo would fit in magazines.
to see it shorter makes sense as if it was longer it would not fit in the magazine.

also my blueprinted rem 700 with kreiger barrel reads 2.773 with a stony coal gauge. i also back of 0.015 for a jump. so my coal is 2.758 and i get under 0.5 moa groups.
155gr scenars
45.2 gr 4064
lapua brass neck sized .335
cci 200 primers


sorry for outrageously huge picture and stupid double post.
GMhHyHV.jpg
 
Do either of you have chamber marks on your sub .5moa rounds as well? I'm wondering if I should slowly seat the round deeper just enough so that the bullets don't engage the rifling.
 
the SMK is a VERY jump tolerable bullet, seat it .015 off the lands and your good to go, continue playing with power charge to find your load. then play with seating depth, for what its worth when i use the SMK starting .015 off, often i find little to no difference with different COAL once i have found my powder charge
 
2.800" is the max OAL with the bullet(SAAMI specs have nothing to do with military mags. They do have to do with ammo fitting chambers.). Loading a bit shorter won't hurt anything. May not be 15 thou for your rifle, but that'll do to start.
Mind you, something isn't correct if you're getting rifling marks on the bullet. Likely how you're measuring something. Probably the OAL. The bolt close easily on your DP cartridge too?
 
Each gun is different. Load ammo in 5 round batches at 2.800" and then in 10 thou increments, deeper, all the way to 2.740", and shoot them.

See if it makes any difference. I prefer the SMKs at about 20 thou off the rifling, or more.
 
Last edited:
Just curious, I guess - the bullet in your picture has a cannelure. Sierra Match King .308 168 Hollow Point Boat Tail (Sierra #2200) bullets do not, at least the ones that I have bought. Could it be that there has been a mix-up regarding what your bullets are?
 
Potashminer said:
Just curious, I guess - the bullet in your picture has a cannelure. Sierra Match King .308 168 Hollow Point Boat Tail (Sierra #2200) bullets do not, at least the ones that I have bought. Could it be that there has been a mix-up regarding what your bullets are?
Click to expand...

Those are the rifle chatter marks that I am referring to. The bullets do not have a cannelure.

sunray said:
2.800" is the max OAL with the bullet(SAAMI specs have nothing to do with military mags. They do have to do with ammo fitting chambers.). Loading a bit shorter won't hurt anything. May not be 15 thou for your rifle, but that'll do to start.
Mind you, something isn't correct if you're getting rifling marks on the bullet. Likely how you're measuring something. Probably the OAL. The bolt close easily on your DP cartridge too?
Click to expand...

The dummy rounds I loaded chamber much easier than the factory Hornaday ammo that the brass originally came from. Those had an AOL of 2.803 as measured from base to tip and didn't have chamber marks when extracted at the range. It seems to me that the Sierra have the ogive much further up towards the tip than the hornady amax bullets.

Will seating the rounds deeper result in significant pressure on the brass that can be considered unsafe? Also, does jumping the bullet lead to decreased barrel life or and premature throat wear at the expense of accuracy?

From my research online it seems that the Savage 10 fcp-k rifles have a tendency of having short chambers.
 
I notice that you are mentioning COAL and chamber length - "short chamber". Not certain if you have a copy of SAAMI chamber specs, but if you did a chamber cast you might want to compare the front end dimensions with the SAAMI specs.
As you know, the 1.640 length that you refer to is the face of the bolt to a point on the case shoulder that is .400" in diameter. You mention in your first post, I believe, that neck sized and carefully trimmed and measured brass chamber fine. That suggests that the chamber, at least to the shoulder is proper, and that the neck diameter is proper. From the SAAMI drawing, the chamber should have it's "neck" extending to 2.025 from the bolt face, with a diameter of 0.3442" at the end of the neck in the chamber. There is a short taper from .3442 down to .310 and then a straight section at .310" out to 2.1388". At that point a 1degree 45minute taper starts, with this final section tapering from the .310 down to .308 at 2.3025. With care, you might get some "ballpark" measurements off of the marks on you bullet - I would be leaning towards a "too short" throat / freebore / leade rather than a "too short" chamber. I have never used one, but understand there are throating reamers that can be used that only address the throating area.
 
Seating the bullet deeper so it jumps will reduce pressure. Seating the bullet out so it hits the rifling will increase pressure.

Neither technique has an effect of barrel life. A blue barrel will last you about 2,000 rounds. A stainless will last around 5,000.

As you shoot, throat erosion will require you to seat the bullets longer to maintain the same jump. In 308 I find the erosion is around 5 to 10 thou a season.
 
I'd also be very surprised if you're on the lands at 2.800. That said, there's no substitute for measuring yourself. Lots of ways to do it, but this is one of the easiest.
w ww.youtube.com/watch?v=GmDi7v530Og
Once you've got the measurement, back off 15 or 20 thou and you're good to go. As already mentioned, the SMK is very jump tolerant.
 
To be honest, those marks, to me, look very rough and look far to "everywhere" to be the rifling marks. Your gun has, what, 6 grooves? Or 4? That marking goes all the way around.... I have no idea what that is, but to me that looks far too constant. When I get rifling marks from checking base to ogive length, they are striations that look very much like the lands of a rifle barrel made them. Might be a little scoring here or there from the ejector pushing the round to one side, or from the feed ramp if you loaded it from the magazine, but that just looks odd.

But the idea is, yes, if your dummy came out like that, and the neck was not at its normal tension, then that is where your ogive touches the rifling lands FOR THAT BULLET. You can seat a fair but shorter, just don't do it at the max charge. If you're only going thirty or forty thou shorter than the book spec I wouldn't worry about pressure, but if you're going a hundred thou or a similar large amount, May want to back the powder charge off for the minimum length you intend to test and confirm it isn't over pressure at that depth
 
You must log in or register to reply here.
Back
Top Bottom