View Full Version : Determining bullet seating depth for controlled round feeding firearms

John in Texas
01-01-2013, 01:35 PM
Does anyone have any experience with determining the bullet seating depth for controlled round feeding firearms? I'm trying to determine seating depth for Nosler's 260 grain Accubond in an Interarms Whitworth .375 H&H magnum. The book value for overall cartridge length is 3.600 inches. When I seat a dummy round to that depth and shorter (3.500 inches), the bullet is pushed into the case when fed from the magazine into the chamber. What am I missing here? Determining seating depth is a simple process on non-controlled round feed firearms. What can I do to make this work? Any suggestions or comments?

John in Texas

01-01-2013, 02:42 PM

Whether or not a rifle is CRF has next to nothing to do with seating depth.

Have you checked neck tension? Are you crimping? What is the make/model of reloading dies you are using? Lee? RCBS? Redding?


John in Texas
01-01-2013, 05:24 PM
Sorry Allen. I must not have made myself clear. The CRF action is preventing me from placing the dummy round directly into the chamber without the bullet touching anything and then closing the bolt. Apparently, the bullet is hitting something other than the lands when fed from the magazine and is being forced into the brass. I'm thinking about Sinclair International's bullet seating depth tool. Anyone have any experience with it?
Thank you Allen for your response.
John in Texas

Jim N
01-01-2013, 06:20 PM
The Hornady comparator is the best system I have found. This is one of those "gotta have" tools.


01-01-2013, 06:46 PM
Ok. Gotcha. Are you just trying to gauge the jump to the lands of the rifling to try and somehow improve accuracy?

You should be able to just pull the bolt, fit a dummy cartgridge into the bolt face and run it up through the action into the chamber. You can use a piece of brass with a split neck. If you are lucky, the bullet will press into the brass, eject easily and give you an indication of how much reach you have to the lands. Do this several times with different pieces of brass to verify that the bullet isn't being pulled out by the lands. If you are unlucky, the bullet will lodge in the rifling and you'll have to gently tap it out with a reloading rod. In either event, you might find that the overall length of a loaded round is either too long for the magazine or too long to eject without hanging up on the inside of the receiver.

If you use a round loaded to recommended spec and still have the bullet pushing back into the brass, you've got other issues. Either incorrect neck sizing (too loose) or some funky obstruction/hang-up.

Clear as mud?

Keep in mind that assuming you full-length sized that belted magnum brass correctly, that cartridge is going to index off the belt, not the shoulder.

I wholeheartedly agree with Jim's recommendation of using a comparator, though I prefer the simplicity of Sinclair's hex-nut style bullet comparator for quick stuff. http://www.sinclairintl.com/reloading-equipment/measuring-tools/bullet-comparators/sinclair-hex-style-bullet-comparators-prod34262.aspx

For more precision, I use a Redding Instant Indicator Die with Dial Indicator set up on another nearby press. http://www.sinclairintl.com/reloading-equipment/measuring-tools/case-gauges-headspace-tools/redding-instant-indicator-prod33548.aspx

If it were me, I wouldn't bother monkeying around too much with OAL. Just go with spec and adjust powder.

Here's one of the better primers on precision reloading out there... http://www.accurateshooter.com/technical-articles/reloading/complete-precision-case-prep/


01-01-2013, 10:01 PM
Apparently, the bullet is hitting something other than the lands when fed from the magazine and is being forced into the brass.

John: If the bullet is being forced into the brass by simply feeding it from the magazine, you have neck tension that's too light. The bullet should not move when fed, regardless of CRF vs push feed action. You need a die that sizes the neck to a sufficent tension where the bullet will not move when fed.

01-01-2013, 11:00 PM
Im new here but if I understand your question the only thing between being fed from the magazine to the chamber that would force a bullet deeper into the case is 1. the round is being bumped into the front of the magazine or the feed ramp. If I have misunderstood and the COAL is decreasing after chambering then you are feeding into the lands. Rather than buying a seating depth gauge just make your own.
This can be done by taking a case and making 2 or 3 cuts down the neck wiith a dremel or hacksaw. Then partially seat the bullet. Next place the round into action and slowly close the bolt. Slowly open the bolt while using your finger to keep the round from making contact with the receiver . Measure the COAL and now you know how far it is to the lands.

01-02-2013, 08:32 AM
Why do you need to use the bolt to pull one up out of the magazine? If you insist on testing a loaded bullet this way, you can carefully feed the rim of your case into the face of the bolt from the magazine, but why?
Spend twenty bucks and get the Stoney Point/Hornady modified case setup for your 375. Or spend thirty bucks and add the comparator to the package. Screw the case onto the tool, put the bullet in the case, remove the bolt and do your thing with the Hornady COAL setup, then measure your magazine length capacity. Go from there. Check function after you have determined your COAL from the first two measurements.
I've owned a few Interarms/Mark X Mausers. They are true Mauser actions. Work with the action, not against it, some of them are particular to the bullet shapes they will feed happily.

John in Texas
01-02-2013, 10:07 AM
Elmbow--I don't use a loaded bullet for this procedure, but I hear what you're saying. Thanks for the response.

01-02-2013, 11:17 AM

Maybe I can contribute something here?!

I built .30-06 rifle off of a Turk Mauser action. The intended use was to sling 180gr and 220gr projos with it. One day, having a plethroa of 150gr loaded .30-06 ammo, I loaded up the mahazine with 5 and tried to go to town. The action totally FUBAR'ed the first round. The geometry of the feed lips + the tension of the magazine spring + the shortness of the 150 gr projo (vs. the length of the 180gr projo) simply does not work on this rifle. It feeds 180 grain projos smooth as silk. 150 grain projos catch in the side of the action and never get to the feed ramp - the tip of the bullet is FUBAR'ed beyond use. Not wanting to touch the shaping/altering of feed rails on a Mauser action, I simply stick to 180 grainers and up for this rifle. (If you file off just a little too much metal, you get to weld back up the rail, then file it off again - no interest in this kind of fun.)

Your description sounds like maybe this could be what is going on?

With the CRF, you ARE supposed to feed only from the magazine, as the extractor can be damaged snapping over the case rim if you single feed into the chamber. This said, I have done exactly this with several Mausers before I knew any better and did not suffere said extractor damage.

I concur with the above input that it sounds like you need to crimp the bullet more also.

Hope this helps some.


01-02-2013, 12:03 PM
Elmbow--I don't use a loaded bullet for this procedure, but I hear what you're saying. Thanks for the response.
I didn't mean loaded like with primers and powder. You sasid you were trying to feed a loaded with bullet case into the action to determine COAL.

Determining your COAL has nothing to dowith CRF or PF. Take out the bolt, put in your bullet,tap it up tight against the lands, gently push a cleaning rod with a flat face on it down the bore until it touches the bullet, mark the rod at the muzzle, take out the bullet, close the bolt,push the rod up to the bolt, re-mark the rod, measure and back off .020". that's the really old school cheap way.
Better: Do what i said in my first post. Like USMA84DAB said. military mauser actions, which is what the Whitworth is, can be picky as to bullet shapes when it comes to feeding. Again, this has nothing to do with COAL.

01-02-2013, 05:03 PM
Another Midway product to consider is the Cartridge Overall Length Gage (http://www.midwayusa.com/product/190644/frankford-arsenal-cartridge-overall-length-gage).

It uses a cleaning rod and two small clamps to measure the distance from the bolt face to the tip of the bullet.

This picture is a little misleading as it shows the result from using the product and not the method to measure the distance.http://media.midwayusa.com/productimages/440x330/primary/190/190644.jpg
From the product web page linked above:


Install the appropriated caliber size tip on the end of the cleaning rod (sold separately).

Insert the cleaning rod down the barrel until there is contact with the bolt face then install one clamp.

Remove the bolt and drop a bullet (projectile only) into the chamber.

Hold the bullet against the rifling with a pencil, touch the bullet tip with the cleaning rod tip and install the other clamp.

Now measure the inside distance between the two clamps with calipers(sold separately) and record the measurement.

The measurement taken can be used as a gage to check the seating depth setup during the reloading sequence and will tell you the maximum length you can seat bullets until the hit the lands of the rifle barrel.

You might be able to fashion something similar yourself without having to buy the item.

01-02-2013, 05:33 PM
Interesting problem. I have that exact rifle and just got done shooting some 270 grain Hornadys in it. They were crimped in and I had no issues. Next up some Barnes 270s and again with the crimping, I just can't think there will be an issue. These rigs shoot really well by the way. Every load tested so far is completely adequate for big game. Running RL15. Good luck.

John in Texas
01-02-2013, 07:28 PM
Thanks fellows. It's been very interesting and educational. I should be able to take it from here. Old school and new school solutions. Take your pick.
John in Texas