Seating depth in a long-throated Tikka...

TNBillyEarl · Jan 8, 2022

All - I have just begun to dial in a new 7mmRM T3x Superlight with 160g Accubonds or Partitions. Thanks to FOTIS and Dr. Mike and others, I found on other posts the QL data and such. I have worked my way up to 66.0g of RL-22 where there was a distinct accuracy node. My last 2 3-shot groups at that load had ESs of 20 and 8, with SDs of 8.2 and 3.6. (Just under 3000 ft/sec.) Both groups were .8MOA at 200 yards. But here is my issue:

1. Nosler sets the COAL for this caliber at 3.29"
2. My magazine is designed only for 3.30", but will hold a single longer cartridge due to its design. (So I could have one in the chamber and one in the magazine.)
3. BUT THE DISTANCE TO THE LANDS IS 3.41"!

Do I really start .02 off the lands and make my first depth test at 3.39? Many of you helped me with my short-throated 700. I got that dialed in nicely with seating depth changes. Making the COAL so long on this gives me pause. Please advise. Thanks.

Bill

***edit*** I haven't pulled out my comparator yet, but the distance will be similar... ***edit***

jimbires · Jan 8, 2022

yes , the 66 - 67 grains of RL22 , with a 160 AccuBond , is a known good load in the 7 rem mag .

if you want to be able to feed from the magazine , you have to stay at a length that reliably feeds , or shorter . if you want to try and better your groups you can try working shorter from mag length . I find the AccuBond likes a fairly long jump . if it's not necessary to feed from the magazine , you can load your ammo out longer , and single feed . I'm not sure you'll find better accuracy with a shorter jump , all you can do is test it .

DrMike · Jan 8, 2022

Jimbires has given you excellent advice. The issue is as simple as whether you want to feed from the magazine or whether you are content to single feed your ammunition.

ReloadKy · Jan 9, 2022

I too have a Tikka T3x in 7 Rem mag. Based on my experience in loading for this rifle you can load that at whatever length that you want and they will shoot well. Now that you have your node I would create some loads as long you can effectively hold in your magazine and then work backwards (farther from the lands) until you find the accuracy that you want. I bet you find a load that will shoot.

TXbaldhunter · Jan 9, 2022

That's not too bad of a jump.If it shoots well at max mag box length,work with it there and don't worry that your well off the lands.I have several rifles with the same issue.The worse on I have is a Sako A7 in a 300 Win Mag.To get it to feed from the magazine,the bullet has to be seated below 3.30 and that puts the ogive into the short neck on the case.It didn't shoot worth a crap,bullet tension was so little I would have to crimp the case to keep the bullet from going into the case because I could actually push them in by hand.Screw that.To feed from the magazine,I would have been .250 off the lands.That is a bit too far.It does shoot great as a single shot with an over all length of 3.490,that puts me about .060 off the lands.It seems to me a lot of designers must not be into loading ammo because this would never fly with someone who did.Interesting how well the 7mag shoots with 66.0grs of Reloader 22 and a 160gr AccuBond.That is exactly what all four of my 7mags shoot well with.Another load I found for the 160gr AccuBond is with 67.5grs of Reloader 26.It also shoots well in all my 7mags.It clocks @ 3084fps

DrMike · Jan 9, 2022

RL22 and a 160 gr bullet is classic for the 7RM. The jump of 0.200 off the lands is not as bad as some I've worked with. The AB may just perform very well (as yours apparently does) with what seems to be an "excessive" jump.

SJB358 · Jan 13, 2022

I am with the others that would load to magazine length and work back if needed. Just me, but if a rifle has a magazine, rounds need to feed from it. I can't even hardly experiment with loading longer than the magazine since it interferes with my nervous twitch.

Another point that is sometimes mixed in with bullet jump is concentricity. If your bullet is started straight you'd be surprised what you can get away with for jump.

AFG270 · Jan 13, 2022

SJB358 said:
I am with the others that would load to magazine length and work back if needed. Just me, but if a rifle has a magazine, rounds need to feed from it. I can't even hardly experiment with loading longer than the magazine since it interferes with my nervous twitch.

LOL, I have that same twitch.

jimbires · Jan 14, 2022

if you're working with a decent gun , one that's not finicky .
I believe that accuracy will happen at a few different seating depths . there could be one best , with others being a close second . I've seen this accuracy at different seating more than once , since I've been shooting all my development ammo especially working seating depth first . years ago when I found decent accuracy with a certain powder charge , I stopped working powder and went to seating depth . then as soon as I found an accurate seating depth , I stopped , that was my load . I never went further to see if it could be improved . I thought it only happened once , and I was happy I found it . then I started to keep working powder charges to get velocity up , and see if accuracy could be found at higher velocity , and I found it could . now it's pretty common knowledge that you have a few different powder nodes to work with . I think you'll find this with seating depth too , I'm not sure how wide spaced these preferred depths will be . I've seen this using .005" increments , I've also seen this using .040" increments . so yes , I think , you should be able to get decent accuracy at magazine length , or shorter , all you can do is test it .

TNBillyEarl · Jan 17, 2023

Circling back a year later, and as reference for anyone who found this thread via a search engine:

I ran out of 160g AB trying to get .5MOA. (After that I did find a great load and seating depth for 140g AB with H4350.) By chance this year during deer season I got a bag of 160g blems and picked up where I left off last January. All of the above direction/advice is correct - I just had to test my jump and confirm all the way down. And yes, there were a couple of depths that gave good groups, but .13" of jump is consistent day to day at under .7 MOA. While using the same steps on my 700, I found the Tikka more accurate overall but much harder to find that go-to load.

Again, many thanks to you all. My last 2 confirmation groups below, both .130" off the lands with RL-22.

Bill