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Posted: 5/24/2006 2:09:55 PM EDT
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I finally got a chance to hit the range, and brought my PS90 along with every type of civilian legal ammo. At 25 yd, the sights weren't off much. The reticle was very hard to see, but the sun was reflecting into the rear fiber optic (for the tritium module) and thus I got a nice and BRIGHT half-cross reticle with a HINT of a donut in the center. The recoil was very much like my 24" AR-15 HBAR (12 lb empty) shooting Wolf 223. It wasn't much, but there was still recoil. The muzzle report was similar to .223 Remington. Mag changes were a bit slow, and the brass catcher worked wonderfully. Overall, it's a great and fun range gun but the ammo is a bit pricey 
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The rumor I had heard was that the SS198 would be a 35gr bullet loaded to fire 2200fps from the five seven, so not only should it make ammo significantly cheaper but it seems like it might be the best loading for the 5.7mm caliber yet. |
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Cleaning the PS90: I heard from other 5.7 owners that the ammo is really clean burning. Well, after only 200 rd, the PS90 was fairly gunked up. The breech block had a lot of crud building up in the breech face and ejector "claw". FN doesn't give instructions on detail stripping the breech block (everything's held by rollpins so it doesn't look like regular maintenance is a good idea), so you can only wipe/brush the exterior. FN over-oiled everything at the factory which makes it a pain to clean the polymer frame unless you separate the halves and degrease everything. |
| I'd be interested in seeing where it prints at 100yds. With my .45 carbine I can get around 5-6" groups at that range and not too far below point of aim ( zeroed at 50yds) I know it's not really the engagement envelope envisioned for the PS90 but it's useful info anyhow. |
With SS195LF, it should shoot flat out to 200m. I'll see if I can shoot it at 100 yd next time. At 25 yd, in the standing unsupported position, the PS90 was Minute of 8.5"x11" paper with a few shots hitting dead center. It's a bit more accurate than my Glock, and of course, the craptastic reflex sight wasn't much of a help. You know, the next time I go to the range, I'll use the iron sights to shoot at the target and get back to you on the accuracy. |
Short bullets will be fine in a 1:9 twist. It's the longer bullets that have problems with slower twists, not shorter bullets with faster twists. |
Is that why most 77gr bullets (lead-core, pretty long for .224") won't stabilize properly past 100 yd when fired out of most 1/9 twist barrels? Why didn't FN just use a lead-core 28gr bullet for its SS195? Wouldn't it have been a very short bullet compare to the 28 gr aluminum core bullet? |
Yes.
I don't know, and I don't care. |
Well I do care. I read once that it was because the short bullets cannot stabilize in the 1/9 twist bores, which is why FN went to an aluminum core to optimize the length of the bullet. I suppose the 40 gr lead-core V-Max stabilizes just fine, so they left it as-is (45 gr will stabilize in my 1/9 twist AR barrels). Remember that not all barrels have consistent twist rates, some 1/9 bores stabilize 75 gr just fine, others will keyhole at 100 yd. |
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I have to wonder what a pulled bbl would look like. Can you lathe turn an AR bbl to work in the P90? Might be interesting to experiment with a few different twist rates and bullet weights. I'm really not sold on the 5.7 ballistics at all. I'd be alot more inclined to put down cash on one in a different caliber. Failing the caliber change maybe a better load can be developed? |
Don't believe everything you read. Short bullets don't require fast twists to stabilize; long bullets do.
No kidding. Varmit rounds like the 45gr .223 round really only require something in a 1:12 twist.
Other than "gain twist" barrels, I have never heard of barrels not having consistant twist rates. Now, there is some variation on the twist, ie 1:9 isn't exactly 1:9. It could be 1:8.7 to 1:9.3, or something like that. But the twist is consistant for the individual barrel. Seventy-five and 77gr 5.56mm projectiles tend to be at the upper limits of bullet length for 1:9 twist barrels. And because of the manufacturing differences from barrel to barrel, you might get one that will stabilize those rounds and others won't. Let's take you logic to the other end of the spectrum. The .22lr has a very short bullet. What twist rate does your average Ruger 10/22 have? |
What I meant was the variation on the twist; it isn't exactly 1:9. Bushmaster said their 20" and 24" 1:9 barrels can stabilize 75 gr bullets, but from what others have said on AR15.com, the only way to find out is to shoot it. FWIW, the PS90 bore feels a bit tighter than my AR-15 barrels. Using the 22 cal Otis patch puller, it feels tighter than my relatively new M4 barrel. I wonder if the PS90 bore is actually a tad smaller in diameter, like .222" |
What happens when you use a short and light bullet in a fast twist bore like 20-30gr lead-core .224" through a 1:7 twist bore? Does it stabilize properly? Now what about a 20-30gr lead-core .224" bullet through a 1:9 twist bore? I know 45 gr lead-core .224" stabilizes through my 1:9 twist AR-15 bore, but I've been curious about 40 gr and lighter lead-core bullets. From what I have read, it's about the length of the bullet and not so much just the mass. |
Short light bullets allegedly will spin apart. It doesn't seem to be a problem for 45gr in a 1:7, but supposedly lighter bullets will fly apart. In a 1:9? I don't know. I usually stay away from varmit rounds out of my AR. |
The PS90 has a ~.224" bore with a 1:9 twist. Now, what happens when you use a lead-core 20-30gr bullet? Supposedly it will fly apart. You usually stay away from varmint rounds in your AR, but we're now asking about the PS90. I *read* that FN uses an aluminum core 28gr bullet in the SS195 because it has the right length to stabilize properly w/o flying apart. The M855, IIRC, is slightly longer than a 62 gr full lead-core bullet, and the 1:7 twist barrels were designed to stabilize the longer tracer rounds (according to the Ammo Oracle IIRC). Now, why is this important? I'd imagine that the length of the lead-core 55gr FMJ bullet used in SS193 is probably the same length as the 28gr aluminum SS195 (more or less?) and you can't safely increase the muzzle velocity, otherwise FN would have already done so. Currently, it appears the SS195 and SS190 are the "flagship" defensive cartridges for the 5.7x28 caliber. |
The 5.7x28 PS90 has a 1:9 twist ~.224" bore, firing ~.224" bullets. Am I missing something else that would affect the bullet weight / length and twist rate? |
Velocity is part of the equation, my dear Watson. (I don't have any figures, I don't have a PS90, and I didn't stay at a Holiday Inn Express last night  )
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Good point! We'll just have to wait and see what some of the reloaders come up with 
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