Hey all,

I just purchased my first 550 series "rifle", it's a 553P with a brace!

As I've been doing reading about the 550, I've discovered that the factory swiss barrel twist rates are 1/10 to be maximized for the standard Swiss ammo (63 gr something-or-other).

It appears that firearms for US export with the "-2" (i.e. DASH 2) designation have the 1/7 twist rates.

While I'm on the hunt for a 552 or 553 "-2" barrel, what types of ammo would work with the 1/10 twist rates but the short 8.9" barrel?

On a similar subject, the rifle "officially" is marked "223". I know the Mini-14's will shoot both 223 and 556, but will the 550 series (with original barrel) be able to handle the 556 round? I don't know if the 550 series is truly 223 or 223 "wylde" or really 556 but labeled 223.

I don't want to damage the gun by loading/firing the wrong ammo!

Any feedback would be GREATLY appreciated!

James

I've only shot 5.56 out of my 553. They are definitely good to go.

quote:

Originally posted by Andyb:
I've only shot 5.56 out of my 553. They are definitely good to go.

Can you shoot or have you shot the higher weigh projectiles (69/71)? If so, any keyholing or accuracy issues with the 1/10 twist?

I assume the 55 grain would be fine. What about lower than 55 grain (say 50 grain varmit 223 loads)?

What about 62 grain M885? I know the Swiss load is 63 grain, but I assume the bullet structure is different based on reading (no penetrator, much much thicker jacket).

SigSAN claims accuracy to 300M, but that's with the swiss ammo, known for accuracy due to construction. I'm wondering how the short barrel with the slower twist rate works for home defense for the US.


Thanks!
James

SAN or SIG or is marking or marked commercial export rifles according to CIP standards. This standard does not differentiate between 5.6mm GP90, 5.56 x 45 and .223 Rem. It’s all considered the same. The same rules apply for any military style self loading rilfe made in Europe.
The key for the correct projectile is the Greenhill formula. Mass or weight is irrelevant. All that matters is length of the projectile. So if you want to get something close to the GP90 projectile you have to focus on projectile length. Further information can be found here. http://kwk.us/twist.html
62gr FMJ ball(SS109) is actually pretty close. Not as well as a performer as the GP90 but close and it will not hurt your rifle. An alternative is RUAG 5.56mm Swiss Match. It's a commercially packed GP90.

JDI has Ruag available. Its not inexpensive.

The GP90 is a good round but it only shows its potential when the barrel can provide a Vo of 950m/s.(3115 fps). Short barrel versions like the 552/553 are too short to accelerate the round up to that speed. With an estimated loss in speed of 100m/s in a 553SB, you would need a longer projectile to compensate. The SS109 of the M855 would probably do well with 10” barrel twist IF Vo is in the range of 850m/s (2790 fps) out of the 553 SB barrel. An alternative would be an conversion to an LB or a 551, if GP90 is what you want. If not M855 is fine and safe.

Hornady has a new Black short barrel 5.56 that should be ideal

https://www.hornady.com/ammuni...lock-hd-sbr-black#!/

quote:

Originally posted by PGT:
Hornady has a new Black short barrel 5.56 that should be ideal

https://www.hornady.com/ammuni...lock-hd-sbr-black#!/

Interesting, but keep in mind that the 55x series has a 1 in 10 twist rate which typically works better for lighter weight (aka smaller) projectiles.

Does anyone know the dimensions of the GP90 round as compared to M193 or M855?

What I didn't say in my original post is that I read that the GP90 Swiss round does great as far as accuracy out the 300 M (even with the 9" barrel), but there are some limited reports (one or two websites) that say the round is actually not that effective for "bad guys" because it does not expand/breakup nor does it have a large wound cavity and will actually "pass thru" a target. Similar complaints were made against the M855 round.

I like the Mk262 Mod1 Round as it has a canneleur (sp?) to break up the round but it's obviously a heavier round. Of course, for home defense, I'm not held to the "conventions of war" so something that expands would be great (of course, over-penetration is an issue).

So, back to the topic, what round would fire fine out of a short barrel with a 1/10 twist that would provide better expansion or wound cavity (i.e. better "stopping power") than the GP90 round?

Would the Hornady Black round stability over relatively short (<150M) distances enough to be accurate AND have good "stopping power"?

James

PS... sorry, there's a lot in this post...just want to understand what would be best for the 553P...

SigSauer imported 553's use 1:7 barrels actually

quote:

Originally posted by PGT:
SigSauer imported 553's use 1:7 barrels actually

Exactly. All of the M&M and SigSauer imported 553P have 1:7 twist (-2) barrels.

JDI allows you to order a 1:10 twist (-1) barrel, though I’m not sure why anyone would want a 1:10 twist 8.9” barrel.

To the OP, your 553 and all Swiss 55x are 5.56 compatible. Shoot whatever you please through your 1:7 twist barrel. My 552 and 553 shoot 55gr and 62gr equally well. I need to try some 77gr OTM through my 553.

Spare 1:7 twist 552/553 barrels are available on Gunbroker at reasonable prices. Stock up while they’re cheap, though you aren’t likely to need a new one. Also, the ones you’ll find on GB will have been pulled from demilled ex-PD 552s, which have 14x1 LH metric muzzle threads vs. the 1/2 x 28 on 553P imports.

Thanks Josh!!!

Everything I kept reading was indicating the 1/10 twist rate. My gun is a 553P imported after M&M and marked Sig SAN but does have an aluminum lower.

I would have thought the bound-for-the-US guns would have had something other than 1/10 based on what our generally available ammo is, but I'm glad to know it was intentionally done.

James

quote:

Originally posted by JoshNC:

quote:

Originally posted by PGT:
SigSauer imported 553's use 1:7 barrels actually

Exactly. All of the M&M and SigSauer imported 553P have 1:7 twist (-2) barrels.

JDI allows you to order a 1:10 twist (-1) barrel, though I’m not sure why anyone would want a 1:10 twist 8.9” barrel.

To the OP, your 553 and all Swiss 55x are 5.56 compatible. Shoot whatever you please through your 1:7 twist barrel. My 552 and 553 shoot 55gr and 62gr equally well. I need to try some 77gr OTM through my 553.

Spare 1:7 twist 552/553 barrels are available on Gunbroker at reasonable prices. Stock up while they’re cheap, though you aren’t likely to need a new one. Also, the ones you’ll find on GB will have been pulled from demilled ex-PD 552s, which have 14x1 LH metric muzzle threads vs. the 1/2 x 28 on 553P imports.

quote:

Originally posted by James in Denver:
Thanks Josh!!!

Everything I kept reading was indicating the 1/10 twist rate. My gun is a 553P imported after M&M and marked Sig SAN but does have an aluminum lower.

I would have thought the bound-for-the-US guns would have had something other than 1/10 based on what our generally available ammo is, but I'm glad to know it was intentionally done.

James

quote:

Originally posted by JoshNC:

quote:

Originally posted by PGT:
SigSauer imported 553's use 1:7 barrels actually

Exactly. All of the M&M and SigSauer imported 553P have 1:7 twist (-2) barrels.

JDI allows you to order a 1:10 twist (-1) barrel, though I’m not sure why anyone would want a 1:10 twist 8.9” barrel.

To the OP, your 553 and all Swiss 55x are 5.56 compatible. Shoot whatever you please through your 1:7 twist barrel. My 552 and 553 shoot 55gr and 62gr equally well. I need to try some 77gr OTM through my 553.

Spare 1:7 twist 552/553 barrels are available on Gunbroker at reasonable prices. Stock up while they’re cheap, though you aren’t likely to need a new one. Also, the ones you’ll find on GB will have been pulled from demilled ex-PD 552s, which have 14x1 LH metric muzzle threads vs. the 1/2 x 28 on 553P imports.

Definitively 1:7 twist. Enjoy!

Question - will a US made bolt and bolt carrier will work in a Swiss gun?

Yes

Thanks!

Last year I purchased 2 X 500 rounds cases of Austrian Hirtenberger SS109 it came on 10-round stripper clips sealed cellophane. The ad stated that it was 62 grain but had a longer projectile than typical NATO ammo.

When I first got it I was really disappointed in its performance but I'd bought it to keep for long term because of the way it's packaged.

Now, reading this thread I think it will be the perfect ammo for my newly acquired 550-1SP

quote:

Originally posted by kimberkid:
Last year I purchased 2 X 500 rounds cases of Austrian Hirtenberger SS109 it came on 10-round stripper clips sealed cellophane. The ad stated that it was 62 grain but had a longer projectile than typical NATO ammo.

When I first got it I was really disappointed in its performance but I'd bought it to keep for long term because of the way it's packaged.

Now, reading this thread I think it will be the perfect ammo for my newly acquired 550-1SP

You should try some and see how it shoots in your -1. Longer projectile length may require faster twist to stabilize.

James-in-Denver not sure if this will actually help in your bullet selection but here are some results from my 550-1 (i in 10 twist)

First of all, I don't know why I keep thinking my 2 cases of Carl Gustav Swiss ammo is Hirtenberger but it is not, however the case does say "NATO SS109 compliant".

I took the 550-1 out Monday for the first time and shot 5 types of ammo, shooting 3 shot groups with a total o f 9 rounds each of each type; my hand load which is a molly coated 69 grain Sierra on 24 grains of BLC-2, the others are all 62 grain; Carl Gustauv; ZQ1 (MKE); SS109 green tip and finally Wolf steel case poly coat. I still want to try some 62 grain Silver Bear because its been a great plinking ammo ... inexpensive and fairly accurate (under 1.5" at 100 yards) in my 556, AR's and HK53 clone ... I would have loaded some but I only have 5 20 round Swiss mags.

To the business!

The factory scope is the Hensoldt 4 power with the model 1 reticle.

Citidel said the scope was sighted in so I didn't make any adjustments, and besides I was just testing ammo. I was shooting at 100 yards and aiming at the center bottom of the black of the target. The target is 8.5x11 "copy paper" the white 8 ring runs off both sides of the paper, then 9 ring is a 6.5" black circle, the 10 ring is 3.5", and the X-ring is 1.25" .

My handloads grouped the best but were in the upper left corner, and some were off the paper; 4 were touching but the entire group was 2.5".

The Carl Gustav is on the left side mostly in the 8 ring sort of stringing vertical 4 1/8",but keep in mind I was shooting 3-round groups alternating brands trying to keep the barrel temp relatively equal ... I started with 10 rounds in each mag and forgot to pull the 10 round when I started, and once again this ammo has disapointed me. I think I'll just put it on belts for my MCR AR upper ... I don't want it mistaken for anything accurate.

Third was the MKE group, 3.5" discounting the flier; 2 at 10:00 in the 9 ring, 3 in a triangle the 10 ring and 2 X's ... somewhere in the 3 sets I pulled 1 @ 10:00 on the outer edge of the 8 ring but I don't remember which set.

The green tip, except for the 2 fliers is the best centered but still scattered, while mostly in the black, 1-X, 3-10's, an 8ring at 8:00 and 7ring at 11:00 ... I'm not sure if they're fliers or not, I may or may not have pulled them, I should have made notes but the wife was waiting at home to go to a movie with another couple and towards the end I was feeling a bit rushed.

And lastly the the Wolf; 2 in the 8 ring at 10:00 and one slightly off the edge, 4 in the 9 ring stringing horizontaly from 10:00 to 2:00 then 2 in the 10 ring at 9:00 and 10:00

I think my next trip I'll use one of my BT mounts with a Leupold 4-12x40 I have on the shelf waiting for a rifle ... Just to see if that makes a difference ... and take some Silver Bear!

Anyway, here's the groups:

quote:

Originally posted by kimberkid:
here are some results from my 550-1 (i in 10 twist)

First of all, I've never shot any 55x series rifle. But I had assumed they were accurate rifles, especially with match-grade bullets such as 69 SMK.

If this were my rifle, the posted targets would be......disappointing. At best. Every AR barrel I've owned -- lengths 14" to 24", twists of 1:9 to 1:7, DI and piston -- has shot 69 SMK very accurately. As in 1-1/4" or less at 100 yards, even on my bad days. Using budget 4x Vortex, uber-clear NF 16x glass, and a handful of optics in between.

Even the groups from the cheaper ammo are large.

with all respect to the shooter, but these results relate to a flitching the two stage trigger, not the ammo. With consistent load and an SS109 projectile it's possible to stay with ease within 1.5 MOA (1.2MOA with GP90). There should not be a problem to place a group into the x rin of this target regardless what ammo you ar using. I recommend some instruction from somebody who's having experience wiht two stage trigges. Such know how is found in small bore or air rilfe teams.