Need Seating Depth Help!

[Tha Gunson]

I recently did a work up to shoot 77gr TMKs out of an AR using data from the Hodgdon site for 77gr SMKs. COAL is 2.260 and the max COAL I'm comfortable with for feeding is 2.265. The problem is, I did some measuring and if I seat the bullet any deeper than 2.260 the case mouth is going to extend beyond the shank and over the ogive because the ogive is longer on the TMKs. I tested loads with lengths of 2.255 (before I realized this) and 2.265. The shorter loads were all more accurate and I'd like to test even shorter, 2.230-2.245. Is this going to create any problems for me at all? I reached the max load for varget and have no signs of high pressure and am getting velocities of about 2620 out of a 20" barrel. I don't know how neck tension plays into this. Do I need to go to a shorter bullet or shorter ogive length bullet? I have some SMKs which would give me a little more wiggle room but I don't want to drop in ballistic coefficient if I don't have to. I'll take any feedback, thanks!

 

[Comrade Terry]

I don't have an answer for you, but want to say "Welcome Aboard".

 

[Texan]

Is 2.260 the COL that Hodgdon recommends?

If you do go deeper, reduce charges and work back up for the chosen depth so that you don't have a big surprise.

As far as the ogive below the case mouth...

I push a sampling of completed rounds with a good amount of force against the side of my bench to make sure neck tension is adequate.

If I seated a bullet with it's ogive 0.030" below the case mouth and it still fed well, and it passed the push test without setback, I don't think I'd personally have a problem with it.

You could likely trim your brass a bit shorter to minimize or eliminate the gap if it affects feeding.

 

[Shynloco]

OAL is always a challenge when dealing with a Gas Gun (or any other rifle for that matter). But the 77gr SMKs are also the most accurate bullet I've found. I have a custom built STT AR15 that has mostly JP Precision parts. When I was working up accurate loads, I tried 55's, 69's that were even better but then the 77's blew away the 69's. BTW, I was using VVN140 and not Varget. But regardless, my best accuracy was when I exceeding the magazine length, but of course, had to hand feed each round. So there's a point when you have to come to terms of the POSSIBILITY that you particular rifle may not shoot the best when magazine feed. SO if need to use the magazine, you might have to compromise and find the load (and bullet) that your rifle will perform the best.

BTW, welcome aboard and have fun. Remember, the "challenge" is part of the fun and every rifle is different. What works in one, may not work in another. So listen to what people say...but on the end, YOUR baby will tell you what she wants to sing sweet.

Alex

 

[T-shooter]

You need larger mags to load longer. The Korean H&K knock-offs will accept a 2.300" COL. This will also give you a little more room for powder. The H&K style has the ends butt-welded instead of overlapped and spot welded. The ASC mags are suppose to take a 2.300" round but some don't. I bought 6 and only 2 would all the way down without work. All the H&K style will but the problem I had was this indentation that went into the feeding lips. I only use Federal brass in my AR and is possible other brands may be better. The extractor groove would catch on the inside and make feeding difficult. I took mine and flattened the inside right at the top with a rounded punch. They feed perfect now.

 

[Tha Gunson]

Thank you all for your input! I stopped getting notifications for some reason so I didn't even see you all responded.

 

[Rsadams]

The matchkings like a jump normally.. just find how much or little is the key..as alex said unless you want to load one round at a time because of mag limits you will just need to play around some.. load 5 at one length 5 at another and so one and do a ladder test until you find what you want. Then load 20 at whatever length works best ,test and refine... Welcome..

 

[Clancy]

Ladder test with seating depths?

New to me.

 

[Fast14riot]

If you're using metal mags, you can cut out the front to allow longer rounds too.

 

[Tha Gunson]

If you're using metal mags, you can cut out the front to allow longer rounds too.

Ive filed a little bit of pmag to get me about an extra .010" or so. But why do you suggest metal mags and how do you mean "cut out the front"? Thanks

 

[Fast14riot]

Like this. Metal mags are stronger after this mod.

http://www.cavitybackbullets.com/product-p/cb-pri-mod-5.56.htm