7 SAUM Seating Heavies Long

[Rijoh]

Newbie question - how much benefit/velocity do you get from loading heavies long to get more case capacity? I have a 7 SAUM (Tikka/Proof) and have hand loaded a range of bullet weights like the 145 LRX, 168 & 175 ABLR to SAAMI specs with good results. Also tired the Berger 195. Berger recommended a COAL of 2.935 using RL26.

Was reading the seating depth article on Berger's site https://bergerbullets.com/shoot-better/shooting-knowledge/measuring-coal-and-cbto/ and this line got me thinking. the extra powder you can add to a cartridge with the bullet seated long will allow you to achieve greater velocity at the same pressure than a cartridge with a bullet seated short.

Using Gordon's Reloading tool I plugged in the numbers to see how many max grains gets me to SAAMI or CIP pressure limit. When I adjust the seating depth to a larger coal it drops the pressure curve and case fill automatically. Adding more grains of powders brings me back to the same pressure limit. But velocity stays within a few fps as the previous and no increase. It was roughly 1 grain more depending where I input the coal.

So is this just an issue with GRT vs real world? I know I'm missing something in this equation and just can't seem to wrap my head around what it is. I'm wanting to understand this before trying and then will work up slowly.

 

[nealm66]

I've always thought the pressure can vary depending on a few things. I believe Roy weatherby figured out a lot of jump can allow more powder with less pressure but there needs to be good neck tension to avoid secondary pressure spikes when the bullet meets the lands. I've also been lead to believe that if jamming, to use a low starting point. I usually do my pressure test 20k from jam and allows me to work in or out for seating ladders and I run 1-2 grains below what I deem as max which allows me to fine tune with .001-.002 ladder if I choose. Hope this helps and is accurate info

 

[nealm66]

Also, barrel length must be considered if trying to gain velocity with slower powders

 

[QuietTexan]

COAL of 2.935

This is already longer than the SAAMI COAL of 2.825". The part you might be missing is the part that probably doesn't apply in your specific case based on this longer COAL: how much more powder you can add from seating longer depends on how far the bullet is intruding on the powder column to begin with. If you aren't already, there's not much gain. When you run it in GRT, how much additional case fill % become available?

A 300 RUM is a good example of gains that can be had from seating longer because in factory form with a 3.600" COL about a third-to-half of the bearing surface is below the neck/shoulder junction, and the entire boat tail is below the shoulder/body junction. When I push the bullet out out to 3.820" there's a significant amount of case volume freed up now that the boat tail is at or above the neck/shoulder junction.

In the real world for this particular bullet/case combo going from 0.130" off the lands to 0.010" off the lands (0.120" further out of seating) gained 50 FPS at the same charge weight, or about 5% increase in case volume, depending on how you want to look at it. I gained about 4gn of additional powder space using 7828 SSC.

 

[Rijoh]

That makes complete sense to me about how much the bullet was inserting into the powder column to begin with. Thanks!!!

One other thing - there seems to be a step from manufacturer's load data to Gordon's and then sometimes another step before you start seeing pressure signs in real life. Sometimes real world pressure signs show up way passed the SAAMI/CIP specs but it seems like many people do it this way.

I've reloaded for only a couple of years and have done ladder tests and have worked up to pressure signs so I know what to look for. Like anyone else, I just want to find the accuracy node first and velocity second. But sometimes that is past book safe. As long as I'm not seeing pressure signs it should be good right?

 

[JasonAL]

Tagging in. I have a Proof tikka prefit 7 SAUM also. I believe the chambers on these are SAAMI spec, thus you will hit the lands loading heavy bullets longer based on the CBTO measurements.
Most I've seen running the 175gr and up on the SAUM are with longer throats chambered to run heavies to full potential. As in a medium or long action instead of a true short action.

 

[Londerko]

I run a 180 hybrid in a Saami chamber.
They touch the lans at 3.025
I load them to 3.010 and still fit 64gr of H1000 in the case with room to spare.
I'm also using a Tikka action

 

[QuietTexan]

Like anyone else, I just want to find the accuracy node first and velocity second. But sometimes that is past book safe. As long as I'm not seeing pressure signs it should be good right?

I'm a big proponent of run big things easy rather than small things hard. Pressure is pressure whether you see it or not, you can change brass before seeing any common pressure signs - a simple clicker can mean a case is toasted. So yes I run up ladders for pressure to find the top in my rifle and maybe QL spits out pressure numbers that are kind of scary for those loads, but once I find the top I load below that by a very comfortable margin in an accuracy node. Basically I won't run a fast node that's at max, I'll run the next one down.

 

[BASE424]

I've always thought the pressure can vary depending on a few things. I believe Roy weatherby figured out a lot of jump can allow more powder with less pressure but there needs to be good neck tension to avoid secondary pressure spikes when the bullet meets the lands. I've also been lead to believe that if jamming, to use a low starting point. I usually do my pressure test 20k from jam and allows me to work in or out for seating ladders and I run 1-2 grains below what I deem as max which allows me to fine tune with .001-.002 ladder if I choose. Hope this helps and is accurate info

What are your thoughts on sa or la for the SAUM?

 

[Londerko]

If you are using a Tikka action for a 7saum there is no reason not to use a LA bolt stop/magazine combo. Zero weight penalty.
Then you can pretty much run any bullet at any length and be fine

 

[nealm66]

What are your thoughts on sa or la for the SAUM?

I'd probably have a conversation with a builder that has experience with the feeding. Myself I'd want LA but if it's a pita to get it to feed right I'd probably wait to see what the new 7prc will be. This be because I have a few cartridges that are keeping the itch down but definitely a cartridge I have thought about for some somewhat local shooting competitions out to 1600 yards with a fairly quick rate of fire and rules of weight and max cartridge size no more than 300wm

 

[QuietTexan]

What are your thoughts on sa or la for the SAUM?

I bought a LA for 7 SAUM.

IMO if you can get something to feed from a LA there are no upsides to choosing SA, only limitations on length. The weight savings between SA and LA is measured in ounces, just take a leak a little more often while hiking and insta-presto you drop a pound from something you have to haul 24/7 and can't set down.

 

[mooredj]

I know this thread is a little old but I will reply anyways.

I like the controlled feed of the Zermatt Arms TL3 that I own. I have no issues with it feeding 6.5 PRC and I don't believe it will be an issue with the 7 SAUM either. The other thing is that I can buy prefit barrels and change from one caliber to another in a few minutes including a bolt head swap if needed. Very versatile action to work off of.

 

[Mike D Texas]

Unknown Munitions has changed the game on short action. They are building a short action DBM that allows 3.150" in the magazine that fits a standard M5 inlet and a Wyatt's cut load port.