Seating depth dilemma

Starting out loading for my Model 7 7mmWSM. Projectile of choice is 150gr. ABLR.

Measured the max. cartridge base to ogive length for my chamber using the split-neck case method and got 2.305”. That seems really long - the factory Precision Hunters are 2.185” CBTO and they’re too long for my magazine.

Until measuring, I thought the PH’s were too long for the chamber as well because the bolt is really stiff to close on them. I assumed I was jamming them into the lands, because I don’t get that with Fed Fusions or PowerShoks.

Back to the ABLRs…To fit the mag I’d need to seat them to 2.175” CBTO. That’s 0.130” jump. Seems way too much to me. I could single-feed until I can get the magazine modified…

I was planning to start at 0.040”, so 2.265” CBTO. That puts only 0.265” of bearing surface in the neck though, so I need to add 0.020” to achieve the rule-of-thumb of at least the calibre.

Where do the forum gurus think I should start? 0.060” jump, 0.130” or somewhere in between?

Id start at mag lenght and work back....who knows it may just shoot

Unless you don't want to use you mag and turn your rifle into a single shot don't seat over the recommended COAL, even if that means a .130" jump. I don't know exactly what the jump is in 303's but I'm sure its more than .130", depending on projectile.

Start at mag length.

Use jump friendly bullets, can't say what they are yet as I've just started with 7mm's myself but considering how jump tolerant some projectiles like Barnes are, I would not worry too much.

Furthermore, since it's a Mod 7, I'd be inclined to stick with what the mag box can fit (2.8" odd IIRC), didn't think you could extend them much more!

The ABLR from common reporting seems to be a fussy projectile that often doesn’t like being close to the lands anyway. Try them at mag length and see how you go.

Have just gone through this with my 7mm08 mod 7 I didn't even bother measuring maximum CBTO as I new I wouldn't get anywhere near it with the limited mag length of a mod 7.
I also dont think there is much if any more length to be gained by modding the mag box.
Another issue you will have with using a long projectile like the ABLR is that to seat it at mag length it will take up room in the case limiting powder capacity.
That being said my 708 using 150gn eldx seated at mag length shoots fantastic so it is possible you may get the ABLR to shoot even with a big jump.
If the ABLR don't work mabey the eldx would be worth a shot, whatever pill you use I dont think you will be able to seat it anywhere near the lands without single feeding due to the short mag length of the mod 7.
That shouldn't stop you from getting awesome results.

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Originally Posted by mopheadrob

Starting out loading for my Model 7 7mmWSM. Projectile of choice is 150gr. ABLR.

Measured the max. cartridge base to ogive length for my chamber using the split-neck case method and got 2.305”. That seems really long - the factory Precision Hunters are 2.185” CBTO and they’re too long for my magazine.

Until measuring, I thought the PH’s were too long for the chamber as well because the bolt is really stiff to close on them. I assumed I was jamming them into the lands, because I don’t get that with Fed Fusions or PowerShoks.

Back to the ABLRs…To fit the mag I’d need to seat them to 2.175” CBTO. That’s 0.130” jump. Seems way too much to me. I could single-feed until I can get the magazine modified…

I was planning to start at 0.040”, so 2.265” CBTO. That puts only 0.265” of bearing surface in the neck though, so I need to add 0.020” to achieve the rule-of-thumb of at least the calibre.

Where do the forum gurus think I should start? 0.060” jump, 0.130” or somewhere in between?

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Greetings mopheadrob,
I have a Remington 700 Sendero in 7mm SAUM that I regrettably have not done much with. I have measured the cartridge overall length for a number of projectiles with them touching the rifling. Max to seat in the mag is 71mm.

Remington corelokt 150 grain. Crush length 72mm. Jump 1mm
Hornady 139 grain Interlock. Crush length 72.25mm. Jump 1.25mm
Hornady 139 grain SST. Crush length 73.5mm. Jump 2.5mm.
Speer145 grain SP. Crush length 74.5mm. Jump 3.5mm.
Hornady 162 AMax. Crush 75mm. Jump 4mm.
Nosler LRAB 150 grain. Crush 76.2mm. Jump 5.2mm.

I note that the ogive is barely out of the case mouth when seated to mag length with the LRAB in your rifle and has minimal seating depth when loaded close to the rifling. Lengthening the mag will only fix one of these problems. Perhaps a different projectile could be considered depending on the use you have for the rifle.
Regards Grandpamac.

LRAB's like a jump, don't worry about it and work on a mag length that feeds well.

I had a hard time making .222 accurate with reloads. Unheard of eh, you cant Make a .222 inaccurate, so they say. It was accurate with Privi, so I copied their length ogive-to-lands, and it shoots lights out. Miles bigger jump than All the 'experts' (all across the Planet) are saying. Forget about 'the-jump', and go with what works ,with all the tips that others have given above.

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Originally Posted by rewa

I had a hard time making .222 accurate with reloads. Unheard of eh, you cant Make a .222 inaccurate, so they say. It was accurate with Privi, so I copied their length ogive-to-lands, and it shoots lights out. Miles bigger jump than All the 'experts' (all across the Planet) are saying. Forget about 'the-jump', and go with what works ,with all the tips that others have given above.

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funny as heck...SOME of us use a factory load that rifle likes and set up seating die using that...and have done so for 30 years......


if you want close to lands ,and within mag length,use a round nose LMFAO.....

Try mag length and see how they go. My model 7 saum shot the 168vld’s and 160tmk well at mag length/jumped, better than when I tried to seat them long. There is very little length to be gained trying to extend the mag box in the model 7, looks more hassle than it’s worth. I’m about to work up a load with the 162eldm in a barrel I just got fitted, and going to start seating them 10thou off for a ladder to find pressure, then push them deeper and see how that goes.
Cheers

It's fine to jump .130
I don't have experience jumping the lrabs that far but I know the eldms are not finicky on the jump

Thanks all - seems to be a pretty clear consensus there. Yes @grandpamac, I noticed the projectile was in pretty deep at mag length and wondered about case capacity and also the problem discussed in the recent “loose projectile” thread.

The rifle is intended to be a longer range tops / tahr hunting rig, hence the pointy projectiles. I don’t actually mind the idea of single-feeding too much, I can always have a soft-point in the mag for a follow-up shot if required.

Also not many factory loads available to try in this calibre, and those that are are bloody spendy. Have tried Fed Fusions & PowerShoks and Hornady Precision Hunters. All shot okay but nothing special.

I might stick up a photo of a dummy round loaded to mag length next to a couple of factory rounds and see what you guys think, but it sounds like I should be okay.

First photo (left to right): Fusion, Precision Hunter and LRAB at mag length.

Attachment 175211

Second photo: seating depth to achieve SAAMI spec.

Attachment 175212

I think my magazine must be around 0.025” shorter again than SAAMI; the factory PHs don’t fit.

Greetings mopheadrob,
From the photo's it looks as though the full dia section of the projectile is inside the case neck so if you are comfortable seating them longer and single loading that sounds like a good idea. You could use a load with a slightly blunter projectile as a back up in the mag. This was my intention with the SAUM which I must get back to. The 7mm WSM has a very short neck so seating the start of the boat tail just below the neck is likely a good place to start. The LRAB does hot allow much wiggle room due to the short full dia shape.
Regards Grandpamac.

Many of the Yanks are moving away from loading close to lands anyway. Should be able to tune mag length with powder charge to get node. There is a really good YouTube video around this but I've forgotten the guys name?

https://www.youtube.com/watch?v=oRXlCG9YZbQ Erik Cortina Good Watch

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Originally Posted by flock

https://www.youtube.com/watch?v=oRXlCG9YZbQ Erik Cortina Good Watch

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Yes, that's the one. He's really interesting to watch and breaks quite a few long held myths!

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Originally Posted by stagstalker

The ABLR from common reporting seems to be a fussy projectile that often doesn’t like being close to the lands anyway. Try them at mag length and see how you go.

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Got mine at 40thou clearance from lands to fit mag and they still shoot well

Quote:

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Originally Posted by flock

https://www.youtube.com/watch?v=oRXlCG9YZbQ Erik Cortina Good Watch

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Yeah, had watched that a while ago, hence the plan to start with around 20 - 40 thou jump to find the best charge and then worry about seating depth after that.

Quote:

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Originally Posted by grandpamac

Greetings mopheadrob,
From the photo's it looks as though the full dia section of the projectile is inside the case neck so if you are comfortable seating them longer and single loading that sounds like a good idea. You could use a load with a slightly blunter projectile as a back up in the mag. This was my intention with the SAUM which I must get back to. The 7mm WSM has a very short neck so seating the start of the boat tail just below the neck is likely a good place to start. The LRAB does hot allow much wiggle room due to the short full dia shape.
Regards Grandpamac.

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Thanks @grandpamac, this confirms my thinking. Especially as my once-fired brass is a bit shorter than the SAAMI spec trim length for some reason. I'm still shooting the PowerShoks to build up a supply of brass, so these can be my backups in the mag.