155s in a FTR Chamber
- Thread starter dcali
- Start date
Not optimum, but sierra 2156 love to jump. I bet they will shoot just fine.
i would expect it to shoot great.
Yes, the 2156 works quite well. I have not tried them, so do not know about any other 155 grain bullets. It took 48-49 grains of Varget to get the velocity back up to usable levels.
memilanuk
Gold $$ Contributor
Oofta... that's got to be fun to fit in there! I remember running 47-48 gn N150 behind the B155.5BTs, jumping 50 thou, with barely 90 thou of bearing surface in the case neck - and having to use a *long* drop tube plus vibrate the cases to get it all in there without being unduly compressed.
Ned Ludd
Silver $$ Contributor
In response to Damon's inquiry and to satisfy my own curiosity, I made a table of dimensional values for several ~155 gr bullets, along with those from the 185 Juggernaut for comparison. The BT + BS dimension is measured strictly from the bullet boattail (base) to the end of the bearing surface. The BTO measurement (where available) represents the estimated distance from bullet boattail (base) to the rifling contact point on the ogive. All dimensional and BC values were obtained from "Ballistic Performance of Rifle Bullets", 2nd Ed., Bryan Litz, 2015.
Pretty amazing how length difference there is in this weight class of bullets. As watercam suggested, the Scenars are certainly much longer than any other 155 offerings. Even so, by comparison to the 185 Juggernauts, you'd still have very little shank left in the neck with either of the Scenars if they only tuned in relatively close to the lands (i.e. </= .030" off). After looking through the table, my gut feeling tells me the best choice is simply going to boil down to which of these bullets tolerates a pretty long jump the best, because you're not going to be able to seat any of them anywhere close to touching the lands with that much freebore. The BCs, although not identical, are reasonably close, so your two major considerations are going to be seating depth optimum, and how much case volume you have left at whatever the optimal seating depth happens to be. If you decide to pursue loading these and case volume/powder charge/fill ratio does become an issue, you might want to give H4895 a try. It typically gives comparable or better velocity than Varget at noticeably lower case fill ratios.
Pretty amazing how length difference there is in this weight class of bullets. As watercam suggested, the Scenars are certainly much longer than any other 155 offerings. Even so, by comparison to the 185 Juggernauts, you'd still have very little shank left in the neck with either of the Scenars if they only tuned in relatively close to the lands (i.e. </= .030" off). After looking through the table, my gut feeling tells me the best choice is simply going to boil down to which of these bullets tolerates a pretty long jump the best, because you're not going to be able to seat any of them anywhere close to touching the lands with that much freebore. The BCs, although not identical, are reasonably close, so your two major considerations are going to be seating depth optimum, and how much case volume you have left at whatever the optimal seating depth happens to be. If you decide to pursue loading these and case volume/powder charge/fill ratio does become an issue, you might want to give H4895 a try. It typically gives comparable or better velocity than Varget at noticeably lower case fill ratios.
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The 155 Scenar was a popular bullet in the UK in the early days of FTR partly from its history of being number one for 'Target Rifle' (sling) shooting handloaders; partly its high BC; partly availability and cost. (Bergers of various weights and shapes have largely ousted it since here as in the US, at least in the more competitive end of the discipline.)
Back in those days a number of us got Dave Kiff to come up with a chamber that seated the Scenar shallow (no idea of actual freebore in thou') and then found that the 185 Juggernaut shot exceptionally well in it when that bullet was introduced, although I'm sure the freebore and COALs would be rather less than the chamber developed for the US 2013 FCWC team for Raton.
It's still a popular compromise among some of us, ie those who've not succumbed to the ruinously expensive 200.20X affliction. It shoots all 155s from Sierra, Berger, Lapua etc well, the 168 Hybrid and quite a lot more alongside the Juggernaut, even the old 210gn Berger LR BT albeit seated rather deep. Another related change from those early days is the general adoption of much faster twist pitch rates, 1:10 probably the norm for this chamber whereas 1:12 was regarded as 'fast twist' 10 or so years ago.
Ned Ludd
Silver $$ Contributor
IMO - the 0.168 fb chamber reamer designed by Kiff for the Juggernauts is longer than is actually necessary. I shoot them in a chamber with .085" fb, which is about as short as you'd ever want to go. For me, maybe .120" to .140" fb would be just about ideal for the Jugs.
In looking at the dimensions for the various 155 offerings above relative to what I know from loading the Juggernauts and 185 Hybrids in both the short, and relatively long throated (.180" fb) chambers, I'm guessing you'd either be jumping the 155s a country mile, or there wouldn't be a whole lot of shank left in the neck.
That's not to say either of those scenarios couldn't work. However, I'd probably first try to seat them deeper and hope they tuned in and shot well somewhere with a relatively long jump before seating them way out near the end of the neck to keep them closer to the lands. I'm not so crazy about having only a small amount of shank in the neck for a number of reasons, but maybe that's just me.
I'm not sure for what purpose Damon is considering the 155s. I just thought it was an interesting and worthwhile exercise because I don't have a lot of hands-on experience with them.
The chamber was designed for this bullet not the Juggernaut (which arrived on the scene a year or two later). It has maybe a little less than a calibre's shank in the neck at 15 or 20 thou' jump. As I said, we found the Juggernaut gave exceptional performance with it and MVs are fine - 2,825 fps from large primer brass with Viht N550 and the same from N150 subsequently in 'Palma' brass after it was introduced. It shoots a large variety of bullets well, but is no use at all for the heavier Hybrids or I've no doubt the long 200.20X, a bullet I've never tried. Sometime over the coming months, I'll see how the more affordable 195gn Sierra TMK works out in it.
It does have the advantage of flexibility for the clubman who isn't shooting ballistically optimised bullets and loads at long distances all the time. In three or four barrels now so chambered, I'd happily switch from the 185gn Juggernaut in a 2,800 fps plus MV load for a GB league round to using 155 SMKs or better still the 155gn Dyer HBC in spare elderly Norma (LRP) brass at modest 2,800-2,850 fps level and kind-to-barrel loads over N150 in a 500 or 600 yard club competition. It performs outstandingly with Berger's 155.5 BT and 168gn Hybrid (as long as the latter is treated like a VLD and seated into the lands). The latter at nearly 3,000 fps (32-inch Broughton) has won me a lot of medals in 800-1,000 yard comps, or did in the pre 200.20X days, providing the winds weren't too 'hairy'.
Jdne5b
Gold $$ Contributor
In my hands, it requires a longer freebore than the 20x or the new 200smk. It shoots well though.
dcali
Bullet Maker
Interesting feedback. My TR rifle's barrel is not what it used to be, and the rifle is basically a converted Palma rifle anyhow. I thought I'd use it for sling shooting until the barrel just quits, but it's got a long (.200") throat. Sounds like I ought to give a few bullets a try. I'm not expecting miracles (it's a 10 twist, long-throated, half shot out barrel, after all), but if I can get them to shoot even moderately well, I'll be satisfied until I get a new barrel. I'm not a terribly good sling shooter.
In an odd twist, I'm now converting yet another sling rifle for TR use... but I think it will work out better.
In an odd twist, I'm now converting yet another sling rifle for TR use... but I think it will work out better.
135 SMKs love to jump, because they have so much practice.
Ned Ludd
Silver $$ Contributor
Even the 200.20X bullet seems to often "receive" a lot more freebore than it actually requires. Even with as little as .110" to .120" fb, the boattail/bearing surface junction of the 200.20X is still well above the case neck/shoulder junction with the bullet seated at about .010" off the lands. I think it's possible more people could actually load the 200.20X bullet with their existing freebore, but may have been discouraged from doing so by constantly seeing freebore lengths of .180" to .200" reported. If so, that would be a shame because the 200.20X is a very good bullet design, IMO.
You may be surprised just how well some bullets shoot, but you need to do your load development with a chronograph as MVs will be seriously down for any given powder charge and a significant increase will most likely be needed. (As Monte M says above in post #6.)
I'll quote two personal examples akin to yours. My first 'proper' TR rifle was a first generation Schulz & Larsen Mauser '98 based job that had had 20 or so seasons of factory 7.62 ammo through it. Due to throat erosion, freebore was massive - you couldn't get a bullet anywhere near the lands. So I loaded up the longest bullet commonly (and cheaply) available to us at the time, Lapua's D46 185gn rebated-boattail FMJBT barely in the neck and worked up a charge of Hodgdon BL-C(2) that was some 5gn above book maximum. It shot very well for a season and a half until the barrel failed dramatically mid match one day and 1-MOA precision became 4-plus. We didn't have chronographs then, so I've no idea of MVs as a result of the freebore.
Then, more recently I acquired a Paramount TR (sling shooting) rifle sans iron sights as an 'affordable FTR' project to be rebarrelled with a Heavy Palma profile 10-twist barrel. The project never happened for various reasons and I took to plinking with the rifle as was once I managed to get Evo Leisure (the Tier-One people) to design and make a scope rail. The rifle had a 30 or 31-inch Light Palma Lothar-Walther 1:14 twist barrel on it with very 'tight' internal dimensions. Both twist and dimensions point to it having been put on when 144-146gn Milspec 7.62mm NATO ammo was the norm in UK TR shooting, ie many years before and knowing of the previous owner, I know the rifle had been in use for a long, long time with likely a massive round count. (When I asked him direct, he was evasive on the issue, but mutual friends told me how many years this barrel had been in constant use.) As with the Schulz & Larsen, there was massive erosion, but as was common with these rifles used with lower pressure military ammo (especially with the notoriously 'tough' steel in L-W barrels) the eroded throat was smooth and there was no firecracking ahead of it. The then standard GB NRA TR 308 ammo - RWS loaded with the 155gn SMK #2155 to a nominal 2,925 fps in a standard spec TR rifle in good condition would average sub 0.5-MOA 5-round groups off the bench at 100, the best being a single hole (!!) but MVs were WAY down - ~200 fps IIRC.
I shot lots of mild 168gn SMK handloads out of it in this form and it did fine at short ranges despite the 1:14 twist being marginal. The 'trick' with barrels in this condition is to choose very jump tolerant bullets like the old model 155 SMK and 168, 155.5gn Berger etc. I did try the 155 Scenar and it was 'rubbish' - that may well have been the 14-twist, but I suspect also the Scenar's fairly marked secant ogive, even if it isn't a full-house VLD form was a factor. I never measured what the SMKs were jumping, but it had to be well over 100 thou', more likely 200!
(The rifle is still my 'old man's low-cost short-distance range plinker'. It has a recycled 10-twist Krieger on it cut down to 24.75 inches and chambered as a Robinette-design no-freebore .30BR. I'm trying to get 125gn Sierra MKs to shoot well at 100-300 yards and help use up the copious amounts of quick burning powders in my cupboard that I have no use for - Viht N120/130/133; Norma 200; Alliant re7/10x etc, etc.)
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