Quick Question on Mag Length and Seating Depth

[Baron23]

Hi guys - try to keep this short and to the point.

With 1K of 6.5 CM down the tube of my bolt gun, the closest I can possibly get to the lands is .050 off that's at exactly right to max mag length for my MDT binder plate .308 AICS mags which is 2.870.

This doesn't appear to be a real issue as I will be reloading Berger 140 gr Hybrid Targets and all reports seem to indicate that they are very jump tolerant and don't mind jumping quite a bit further.

But, my question is how far off of the mag binder plate so I need to be in order to ensure consistent feeding?

These cartridges will be initially loaded for powder charge testing and I'd kind of like to keep them long and then, after I pick a load to zero in on, I will adjust seating depth to see if I improve the groups.

My current plan is to seat the bullets for a .015" off of mag length with the thought that this would accommodate some variation of bullet length from base to meplat.

Is this enough, not enough, too much (doubtful..haha).

Is there a general rule of thumb as to how far off of max mag length you need to seat in order to avoid any loading feeding issues.

And yes, I will seat some and see how they go in the mags...but thought to ask also.

Cheers

 

[spife7980]

I go with .010 at least, your .015 is just fine.

Load up 10 long and make em shorter until they run without dragging.

 

[Baron23]

I go with .010 at least, your .015 is just fine.

Load up 10 long and make em shorter until they run without dragging.

Thanks. I know, kind of obvious question....well, until you find it wasn’t so obvious and fuck a bunch of stuff up! Haha

thanks again.

 

[spife7980]

I would test and see where it shoots best and try to get it there.
What action are you running? Which is a leading question for: could you run non binder plate mags if the testing shows it likes to be longer?

 

[Baron23]

I would test and see where it shoots best and try to get it there.

Well, I will....after I select a powder charge that I think will get me the MV I want...and hopefully group decently. I've got a long background in test and eval and my mantra is only change one variable at a time.

Then I will start seating the bullet deeper and see what I have. I would not be surprised to find that the Berger 140 hybrid target shoots completely wonderful at .100" off of the lands as some seem to go up to even .150 off.

Action is a Seekins Havak with a Proof SS MTU barrel. I bought the gun with 21 rounds in it (basically, he broke the barrel in if that's even a thing).

I would not have chosen that action if I was building the gun, but it was a great deal and in a pristine JAE and I wanted that chassis so....

As for if non-binder plate mags would work in there....dunno. I do know that MDT cautions that, in some guns, using a non-binder plate mag may req modification to the feed ramp. Don't want to go there and hell.....factory Berger and Hndy are loaded to 2.80 and shoot very well in this gun so I'm not thinking I have to jump all over the lands with this load. But, if I can't find decent performance, perhaps that would be a further investigative step.

 

[spife7980]

You can look into your ejection port and see where the action starts to cover up the mag/binder plate.

Here you can see that the binder plate (tan) keeps the tips well back from the feed ramp but that the front of the mag may be hidden under the lip ever so slightly. See if you can see the front inside of your mag is close to clearing or if it’s way covered up.

 

[KZP]

load one long round into your mag. The top round won't touch the binder plate. Carefully insert the mag as straight as possible. If you feel the bullet get caught on your action it's no go. Look down in like in the photo Spife posted while doing it.

 

[Baron23]

@spife7980 @KZP - thanks guys...got that!

Good image of that on MDT's site that illustrates this.

If my back will cooperate today, I'll start to seat some bullets and see how they feed.

Thanks again for the input....I really like the Reloading sub-forum, great information and helpful people here.

 

[Baron23]

@spife7980 @KZP - hey guys, just following up.

So, this is loaded at 2.859....just about .010 less than max mag length for binder plate mag and there seems to be plenty of clearance in the mag.

And, even at max mag length, I have tons of room before slipping under feed ramp. I could even use non-binder plate MDT mags and longer COAL with no worries but I own binder plate mags already and until and unless I see a need to get a lot closer to the lands than most folks loading Berger Hybrids, I'm thinking I'm just going to stick to what I have in hand right now.

So, my plan is to load up my charge weight test rounds at 2.860, .010 less than mag length, .060 off of lands and see how that goes for a start.

Am I missing a pitfall here or......???

 

[spife7980]

No pitfall other than it just might shoot better seated further out.

But proper load development is the only answer to that question.